Organic electroluminescence element and electronic device

ABSTRACT

An organic electroluminescence device includes an anode, an emitting layer and a cathode, in which the emitting layer includes a first compound and a second compound, the first compound is a delayed fluorescent compound, the second compound is a fluorescent compound, an emission quantum efficiency of the first compound is 70% or less, and an ionization potential Ip1 of the first compound and an ionization potential Ip2 of the second compound satisfy a relationship of 0≤Ip2−Ip1≤0.8 eV.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/546,215, which is a national stage ofInternational Application No. PCT/JP2016/053109, filed Feb. 2, 2016,which claims priority to Japanese Patent Application No. 2015-022731,filed Feb. 6, 2015. The contents of these applications are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an organic electroluminescence deviceand an electronic device.

BACKGROUND ART

When a voltage is applied to an organic electroluminescence device(hereinafter, occasionally referred to as “organic EL device”), holesand electrons are injected into an emitting layer respectively from ananode and a cathode. The injected holes and electrons are recombined togenerate excitons in the emitting layer. According to the electron spinstatistics theory, singlet excitons are generated at a ratio of 25% andtriplet excitons are generated at a ratio of 75%.

A fluorescent organic EL device, which uses emission caused by singletexcitons, is applied to a full color display of a mobile phone, a TV setand the like. It has been studied to further improve a performance ofthe fluorescent organic EL device. For instance, in order to furtherimprove a luminous efficiency, an organic EL device with use of singletexcitons and triplet excitons has been studied.

An organic EL device using delayed fluorescence has been proposed andstudied. For instance, a thermally activated delayed fluorescence (TADF)mechanism has been studied. The TADF mechanism uses such a phenomenonthat inverse intersystem crossing from triplet excitons to singletexcitons thermally occurs when a material having a small energy gap(ΔST) between singlet energy level and triplet energy level is used. Asfor thermally activated delayed fluorescence, refer to, for instance,“ADACHI, Chihaya, ed. (Mar. 22, 2012), “Yuki Hando-tai no Debaisu Bussei(Device Physics of Organic Semiconductors)”, Kodansha, pp. 261-262.”

For instance, non-Patent Literatures 1 and 2 also disclose organic ELdevices using the TADF mechanism.

CITATION LIST Non-Patent Literature(s)

-   Non-Patent Literature 1: Hajime Nakanotani, et al (9 persons),    “High-Efficiency organic light-emitting diodes with fluorescent    emitters”, NATURE COMMUNICATIONS, in May 30, 2014, 5, 4016 (DOI:    10.1038/ncomms5016)-   Non-Patent Literature 2: Dongdong Zhang, et al (6 persons),    “High-Efficiency Fluorescent Organic Light-Emitting Devices Using    Sensitizing Hosts with a Small Singlet-Triplet Exchange Energy”,    ADVANCED MATERIALS, 2014 (DOI: 10.1002/adma.201401476)

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

An object of the invention is to provide an organic electroluminescencedevice capable of prolonging a lifetime, improving a luminousefficiency, and inhibiting a roll-off when driven at a high currentdensity, and an electronic device including the organicelectroluminescence device.

Means for Solving the Problems

According to an aspect of the invention, an organic electroluminescencedevice includes an anode, an emitting layer and a cathode, in which theemitting layer includes a first compound and a second compound, thefirst compound is a delayed fluorescent compound, the second compound isa fluorescent compound, an emission quantum efficiency of the firstcompound is 70% or less, and an ionization potential Ip1 of the firstcompound and an ionization potential Ip2 of the second compound satisfya relationship of 0≤Ip2−Ip1≤0.8 eV (Numerical Formula 1).

According to another aspect of the invention, an organicelectroluminescence device includes an anode, an emitting layer and acathode, in which the emitting layer includes a first compound and asecond compound, the first compound is a delayed fluorescent compound,the second compound is a fluorescent compound, and an ionizationpotential Ip1 of the first compound and an ionization potential Ip2 ofthe second compound satisfy a relationship of 0≤Ip2−Ip1≤0.3 eV(Numerical Formula 3).

According to another aspect of the invention, an electronic deviceincludes the organic electroluminescence device according to the aboveaspect.

According to the above aspect of the invention, an organicelectroluminescence device capable of prolonging a lifetime, improving aluminous efficiency, and inhibiting a roll-off when driven at a highcurrent density, and an electronic device including the organicelectroluminescence device can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows an exemplary arrangement of an organicelectroluminescence device according to a first exemplary embodiment.

FIG. 2 schematically shows a device for measuring transient PL.

FIG. 3 shows examples of a transient PL decay curve.

FIG. 4 shows a relationship in energy levels between compounds containedin an emitting layer and a relationship in energy transfer between thecompounds in the first exemplary embodiment.

FIG. 5 shows a relationship in energy levels between compounds containedin an emitting layer and a relationship in energy transfer between thecompounds in the second exemplary embodiment.

DESCRIPTION OF EMBODIMENTS First Exemplary Embodiment

Arrangement(s) of an organic EL device according to a first exemplaryembodiment of the invention will be described below.

The organic EL device includes an anode, a cathode and an organic layerdisposed therebetween. The organic layer includes one or more layersformed of an organic compound. The organic layer may further contain aninorganic compound. The organic layer of the organic EL device of theexemplary embodiment includes at least one emitting layer. For instance,the organic layer may consist of the emitting layer, or may include oneof layers usable in a typical organic EL device, such as a holeinjecting layer, a hole transporting layer, an electron injecting layer,an electron transporting layer, a hole blocking layer and an electronblocking layer.

FIG. 1 schematically shows an exemplary arrangement of the organic ELdevice according to the exemplary embodiment. An organic EL device 1includes a light-transmissive substrate 2, an anode 3, a cathode 4, andan organic layer 10 provided between the anode 3 and the cathode 4. Theorganic layer 10 include a hole injecting layer 6, a hole transportinglayer 7, an emitting layer 5, an electron transporting layer 8, and anelectron injecting layer 9 which are laminated on the anode 3 in thisorder.

Emitting Layer

The emitting layer of the organic EL device includes a first compoundand a second compound. The emitting layer may contain a metal complex,but preferably contains no phosphorescent metal complex in the exemplaryembodiment.

First Compound

The first compound in the exemplary embodiment is a delayed fluorescentcompound.

An emission quantum efficiency of the first compound is 70% or less. Theemission quantum efficiency of the first compound is preferably 65% orless, more preferably 60% or less. The emission quantum efficiency ofthe first compound is preferably more than 0%, more preferably 30% ormore.

The first compound in the exemplary embodiment is not a metal complex.The first compound is preferably represented by a formula (1).

In the formula (1), A is an acceptor moiety and is a group having apartial structure selected from partial structures represented byformulae (a-1) to (a-7). When a plurality of A are present, theplurality of A may be mutually the same or different and may be combinedto form a saturated or unsaturated ring. B is a donor moiety and has oneselected from partial structures represented by formulae (b-1) to (b-6).When a plurality of B are present, the plurality of B may be mutuallythe same or different and may be combined to form a saturated orunsaturated ring. a, b and d are each independently an integer from 1 to5. c is an integer from 0 to 5. When c is 0, A is bonded to B by asingle bond or a Spiro bond. When c is an integer from 1 to 5, L is alinking group selected from the group consisting of a substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 ring carbonatoms and a substituted or unsubstituted heterocyclic group having 5 to30 ring atoms. When a plurality of L are present, the plurality of L maybe mutually the same or different and may be combined to form asaturated or unsaturated ring.

In the formula (b-1) to (b-6), R is each independently a hydrogen atomor a substituent. When R is a substituent, the substituent is selectedfrom the group consisting of a substituted or unsubstituted aromatichydrocarbon group having 6 to 30 ring carbon atoms, a substituted orunsubstituted heterocyclic group having 5 to 30 ring atoms, and asubstituted or unsubstituted alkyl group having 1 to 30 carbon atoms.When a plurality of R are present, the plurality of R may be mutuallythe same or different and may be combined to form a saturated orunsaturated ring.

A bonding pattern of the compound represented by the formula (1) isexemplified by bonding patterns shown below in Table 1.

TABLE 1 No. a b c d Bonding Pattern (1A) 1 1 0 1 B—A (1B) 1 1 1 1 B—L—A(1C) 2 1 0 1

(1D) 1 2 0 1

(1E) 2 1 1 1

(1F) 1 2 1 1

(1G) 1 1 2 1 B—L—L—A (1H) 1 1 1 2

Manufacturing Method of First Compound

The first compound can be manufactured by a method described inInternational Publication No. WO2013/180241, International PublicationNo. WO2014/092083, International Publication No. WO2014/104346 and thelike.

Delayed Fluorescence

Delayed fluorescence (thermally activated delayed fluorescence) isexplained in “ADACHI, Chihaya, ed., “Yuki Hando-tai no Debaisu Bussei(Device Physics of Organic Semiconductors)”, Kodansha, pp. 261-268.”According to this literature, when an energy gap ΔE₁₃ between thesinglet state and the triplet state of a fluorescent material can bereduced, inverse energy transfer from the triplet state to the singletstate, which usually occurs at a low transition probability, occurs at ahigh transition probability to cause thermally activated delayedfluorescence (TADF). Further, FIG. 10.38 in this literature illustratesan occurrence mechanism of the delayed fluorescence. The first compoundof the exemplary embodiment is a compound exhibiting thermally activateddelayed fluorescence caused by this mechanism. Occurrence of delayedfluorescence emission can be determined by transient PL (PhotoLuminescence) measurement.

The behavior of delayed fluorescence can be analyzed based on the decaycurve obtained by the transient PL measurement. The transient PLmeasurement is a process where a sample is irradiated with a pulse laserto be excited, and a decay behavior (transient characteristics) of PLemission after the irradiation is stopped is measured. PL emission usinga TADF material is divided into an emission component from singletexcitons generated by the first PL excitation and an emission componentfrom singlet excitons generated via triplet excitons. The lifetime ofthe singlet excitons generated by the first PL excitation is in anano-second order and considerably short. Emission from these singletexcitons thus decays immediately after the irradiation with the pulselaser.

In contrast, delayed fluorescence, which is emission from the singletexcitons generated via long-life triplet excitons, decays slowly. Thereis thus a large difference in time between emission from the singletexcitons generated by the first PL excitation and emission from thesinglet excitons generated via triplet excitons. Therefore, a luminousintensity resulting from the delayed fluorescence can be obtained.

FIG. 2 schematically shows an exemplary device for measuring transientPL.

A transient PL measuring device 100 of the exemplary embodimentincludes: a pulse laser 101 capable of emitting light with apredetermined wavelength; a sample chamber 102 configured to house ameasurement sample; a spectrometer 103 configured to disperse lightemitted from the measurement sample; a streak camera 104 configured toform a two-dimensional image; and a personal computer 105 configured toanalyze the two-dimensional image imported thereinto. It should be notedthat transient PL may be measured by a device different from onedescribed in the exemplary embodiment.

The sample to be housed in the sample chamber 102 is prepared by forminga thin film, which is made of a matrix material doped with a dopingmaterial at a concentration of 12 mass %, on a quartz substrate.

The thus-obtained thin film sample is housed in the sample chamber 102,and is irradiated with a pulse laser emitted from the pulse laser 101 toexcite the doping material. The emitted excitation light is taken in a90-degree direction with respect to the irradiation direction of theexcitation light, and is dispersed by the spectrometer 103. Atwo-dimensional image of the light is formed through the streak camera104. In the thus-obtained two-dimensional image, an ordinate axiscorresponds to time, an abscissa axis corresponds to wavelength, and abright spot corresponds to luminous intensity. The two-dimensional imageis taken at a predetermined time axis, thereby obtaining an emissionspectrum with an ordinate axis representing luminous intensity and anabscissa axis representing wavelength. Further, the two-dimensionalimage is taken at a wavelength axis, thereby obtaining a decay curve(transient PL) with an ordinate axis representing the logarithm ofluminous intensity and an abscissa axis representing time.

For instance, a thin film sample A was prepared using a referencecompound M1 below as a matrix material and a reference compound DP1below as a doping material, and transient PL was measured.

Respective decay curves of the thin film sample A and a thin film sampleB were analyzed. The thin film sample B was prepared in the same manneras described above using a reference compound M2 below as a matrixmaterial and the reference compound DP1 as a doping material.

FIG. 3 shows a decay curve obtained from transient PL measured usingeach of the thin film samples A and B.

As described above, an emission decay curve with an ordinate axisrepresenting luminous intensity and an abscissa axis representing timecan be obtained by the transient PL measurement. Based on the emissiondecay curve, a fluorescence intensity ratio between fluorescence emittedfrom a singlet state generated by photo-excitation and delayedfluorescence emitted from a singlet state generated by inverse energytransfer via a triplet state can be estimated. In a delayed fluorescentmaterial, a ratio of the intensity of the slowly decaying delayedfluorescence to the intensity of the promptly decaying fluorescence isrelatively large.

In the exemplary embodiment, the luminescence amount of the delayedfluorescence can be obtained using the device shown in FIG. 2. Emissionfrom the first compound includes: Prompt emission observed immediatelywhen the excited state is achieved by exciting the first compound with apulse beam (i.e., a beam emitted from a pulse laser) having anabsorbable wavelength; and Delay emission observed not immediately whenbut after the excited state is achieved. In the exemplary embodiment,the amount of Delay emission is preferably 5% or more relative to theamount of Prompt emission.

The amount of Prompt emission and the amount of Delay emission can beobtained in the same method as a method described in “Nature 492,234-238, 2012.” The amount of Prompt emission and the amount of Delayemission may be calculated using a device different from one describedin the above Literature.

For instance, a sample usable for measuring the delayed fluorescence maybe prepared by co-depositing the first compound and a compound TH-2below on a quartz substrate at a ratio of the first compound being 12mass % to form a 100-nm-thick thin film.

Second Compound

The second compound in the exemplary embodiment is a fluorescentcompound.

The second compound preferably emits fluorescence having a main peakwavelength (occasionally referred to as an emission peak wavelength) of550 nm or less. Moreover, the second compound preferably emitsfluorescence having the main peak wavelength of 430 nm or more. The mainpeak wavelength means a peak wavelength of luminescence spectrumexhibiting a maximum luminous intensity among luminous spectra measuredusing a toluene solution where the second compound is dissolved at aconcentration from 10⁻⁶ mol/l to 10⁻⁵ mol/l.

The second compound preferably emits a green or blue fluorescence. Thesecond compound is preferably a material exhibiting a high emissionquantum efficiency.

The second compound of the exemplary embodiment may be a fluorescentmaterial. Examples of the fluorescent dopant material include abisarylamino naphthalene derivative, an aryl-substituted naphthalenederivative, a bisarylamino anthracene derivative, an aryl-substitutedanthracene derivative, a bisarylamino pyrene derivative, anaryl-substituted pyrene derivative, a bisarylamino chrysene derivative,an aryl-substituted chrysene derivative, a bisarylamino fluoranthenederivative, an aryl-substituted fluoranthene derivative, anindenoperylene derivative, a pyrromethene boron complex compound, acompound having a pyrromethene skeleton or a metal complex thereof, adiketopyrrolopyrrole derivative, and a perylene derivative.

The second compound of the exemplary embodiment may be a compoundrepresented by a formula (10) below.

In the formula (10), A_(D) is a substituted or unsubstituted aromatichydrocarbon group having 12 to 50 ring carbon atoms. Examples of thearomatic hydrocarbon group having 12 to 50 ring carbon atoms in A_(D)include groups derived from naphthalene, anthracene, benzanthracene,phenanthrene, chrysene, pyrene, fluoranthene, benzofluoranthene,perylene, picene, triphenylene, fluorene, benzofluorene, stilbene andnaphthacene, and further include benzo groups and ring-expanded groupsof the aromatic hydrocarbon groups.

In the formula (10), B_(D) is represented by a formula (11) below.

In the formula (10), pa is an integer of 1 to 4, and pb is an integer of0 to 4.

In the formula (11), Ar₁, Ar₂ and Ar₃ each independently represent asubstituent selected from the group consisting of a substituted orunsubstituted aromatic hydrocarbon group having 6 to 50 ring carbonatoms, substituted or unsubstituted alkyl group having 1 to 50 carbonatoms, substituted or unsubstituted alkenyl group, substituted orunsubstituted alkynyl group, and substituted or unsubstitutedheterocyclic group having 5 to 50 atoms forming a ring (i.e., ringatoms), and pc is an integer of 0 to 4. A wavy line in the formula (11)shows a bonding position with the aromatic hydrocarbon group representedby A_(D).

In the formulae (10) and (11), a plurality of A_(D) may be mutually thesame or different, a plurality of B_(D) may be mutually the same ordifferent, a plurality of pa may be mutually the same or different, aplurality of pb may be mutually the same or different, a plurality ofAr₁ may be mutually the same or different, a plurality of Ar₂ may bemutually the same or different, a plurality of Ar₃ may be mutually thesame or different, and a plurality of pc may be mutually the same ordifferent.

Examples of the compound represented by the formula (10) include thefollowing compounds, but the second compound is not limited thereto. Inthe following compounds, A_(D1) to A_(D4) each independently representthe same as A_(D), and B_(D1) to B_(D4) each independently represent thesame as B_(D).

The aromatic hydrocarbon group in A_(D) is preferably an aromatichydrocarbon group having 12 to 24 ring carbon atoms, more preferably anaromatic hydrocarbon group having 18 to 20 ring carbon atoms. Examplesof the aromatic hydrocarbon group in A_(D) includes a naphthylphenylgroup, naphthyl group, acenaphthylenyl group, anthryl group, benzanthrylgroup, aceanthryl group, phenanthryl group, benzo[c]phenanthryl group,phenalenyl group, fluorenyl group, picenyl group, pentaphenyl group,pyrenyl group, chrysenyl group, benzo[g]chrysenyl group, s-indecenylgroup, as-indecenyl group, fluoranthenyl group, benzo[k]fluoranthenylgroup, triphenylenyl group, benzo[b]triphenylenyl group, benzofluorenylgroup, styrylphenyl group, naphthacenyl group, perylenyl group, andring-expanded group thereof; preferably, anthryl group, picenyl group,pyrenyl group, chrysenyl group, fluoranthenyl group,benzo[k]fluoranthenyl group, benzofluorenyl group, styrylphenyl group,naphthacenyl group, perylenyl group, and benzo groups or ring-expandedgroups thereof; more preferably, anthryl group, pyrenyl group, chrysenylgroup, benzo[k]fluoranthenyl group, benzofluorenyl group, styrylphenylgroup, and benzo groups or ring-expanded groups thereof; particularlypreferably, anthryl group, pyrenyl group, chrysenyl group,benzo[k]fluoranthenyl group, and benzofluorenyl group.

The aromatic hydrocarbon groups in Ar₁, Ar₂ and Ar₃ are eachindependently an aromatic hydrocarbon group having 6 to 24 ring carbonatoms, more preferably an aromatic hydrocarbon group having 6 to 12 ringcarbon atoms. The aromatic hydrocarbon groups in Ar₁, Ar₂ and Ar₃ mayeach independently be any one of a phenyl group, naphthylphenyl group,biphenylyl group, terphenylyl group, naphthyl group, acenaphthylenylgroup, anthryl group, benzoanthryl group, aceanthryl group, phenanthrylgroup, benzo[c]phenanthryl group, phenalenyl group, fluorenyl group,picenyl group, pentaphenyl group, pyrenyl group, chrysenyl group,benzo[g]chrysenyl group, s-indacenyl group, as-indacenyl group,fluoranthenyl group, benzo[k]fluoranthenyl group, triphenylenyl group,benzo[b]triphenylenyl group, benzofluorenyl group, styrylphenyl group,naphthacenyl group and perylenyl group, and benzo groups andring-expanded groups of these groups, among which a phenyl group,biphenyl group, terphenylyl group and naphthyl group are preferable,phenyl group, biphenyl group and terphenylyl group are more preferable,and a phenyl group is especially preferable.

Examples of the substituted aromatic hydrocarbon group include aphenylnaphthyl group, naphthylphenyl group, tolyl group, xylyl group,silylphenyl group, trimethylsilylphenyl group, 9,9-dimethylfluorenylgroup, 9,9-diphenylfluorenyl group, 9,9′-spirobifluorenyl group andcyanophenyl group, among which, for instance, a tolyl group, xylylgroup, trimethylsilylphenyl group, 9,9-dimethylfluorenyl group,9,9-diphenylfluorenyl group, 9,9′-spirobifluorenyl group, cyanophenylgroup and silylphenyl group are preferable.

The alkyl group(s) in Ar₁, Ar₂ and Ar₃ is preferably each independentlyan alkyl group having 1 to 10 carbon atoms, and more preferably an alkylgroup having 1 to 5 carbon atoms. Examples of the alkyl group(s) in Ar₁,Ar₂ and Ar₃ include a methyl group, ethyl group, n-propyl group,isopropyl group, n-butyl group, isobutyl group, s-butyl group, t-butylgroup, pentyl group (including isomers thereof), hexyl group (includingisomers thereof), heptyl group (including isomers thereof), octyl group(including isomers thereof), nonyl group (including isomers thereof),decyl group (including isomers thereof), undecyl group (includingisomers thereof) and dodecyl group (including isomers thereof), amongwhich a methyl group, ethyl group, n-propyl group, isopropyl group,n-butyl group, isobutyl group, s-butyl group, t-butyl group and pentylgroup (including isomers thereof) are preferable, a methyl group, ethylgroup, n-propyl group, isopropyl group, n-butyl group, isobutyl group,s-butyl group and t-butyl group are more preferable, and a methyl group,ethyl group, isopropyl group and t-butyl group are especiallypreferable.

The alkyl group(s) in Ar₁, Ar₂ and Ar₃ may each independently be acycloalkyl group having 3 to 50 ring carbon atoms. The cycloalkylgroup(s) in Ar₁, Ar₂ and Ar₃ is preferably each independently acycloalkyl group having 3 to 6 ring carbon atoms, and more preferably acycloalkyl group having 5 or 6 ring carbon atoms. Examples of thecycloalkyl group(s) in Ar₁, Ar₂ and Ar₃ include a cyclopropyl group,cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptylgroup, cyclooctyl group and adamantyl group, among which a cyclopentylgroup and cyclohexyl group are preferable.

The alkenyl group(s) in Ar₁, Ar₂ and Ar₃ is preferably eachindependently an alkenyl group having 2 to 20 carbon atoms, and morepreferably an alkenyl group having 2 to 10 carbon atoms. Examples of thealkenyl group(s) in Ar₁, Ar₂ and Ar₃ include a vinyl group, allyl group,1-butenyl group, 2-butenyl group, 3-butenyl group, 1,3-butanedienylgroup, 1-methylvinyl group, 1-methylallyl group, 1,1-dimethylallylgroup, 2-methylallyl group and 1,2-dimethylallyl group.

Examples of the substituted alkenyl group include a styryl group,2,2-diphenylvinyl group, 1,2-diphenylvinyl group, 1-phenylallyl group,2-phenylallyl group, 3-phenylallyl group, 3,3-diphenylallyl group,1-phenyl-1-butenyl group and 3-phenyl-1-butenyl group.

The alkynyl group(s) in Ar₁, Ar₂ and Ar₃ is preferably eachindependently an alkynyl group having 2 to 20 carbon atoms, and morepreferably an alkynyl group having 2 to 10 carbon atoms. The alkynylgroup(s) in Ar₁, Ar₂ and Ar₃ may be a propargyl group or a 3-pentynylgroup.

The heterocyclic group(s) in Ar₁, Ar₂ and Ar₃ is preferably eachindependently a heterocyclic group having 5 to 24 ring atoms, and morepreferably a heterocyclic group having 5 to 18 ring atoms. Theheterocyclic group(s) in Ar₁, Ar₂ and Ar₃ may be a heterocyclic grouphaving 1 to 5 hetero atoms (e.g., nitrogen atom, oxygen atom and sulfuratom). The heterocyclic group(s) in Ar₁, Ar₂ and Ar₃ may eachindependently be any one of a pyrrolyl group, furyl group, thienylgroup, pyridyl group, pyridazynyl group, pyrimidinyl group, pyrazinylgroup, triazinyl group, imidazolyl group, oxazolyl group, thiazolylgroup, pyrazolyl group, isooxazolyl group, isothiazolyl group,oxadiazolyl group, thiadiazolyl group, triazolyl group, tetorazolylgroup, indolyl group, isoindolyl group, benzofuranyl group,isobenzofuranyl group, benzothiophenyl group, isobenzothiophenyl group,indolizinyl group, quinolizinyl group, quinolyl group, isoquinolylgroup, cinnolinyl group, phthalazinyl group, quinazolinyl group,quinoxalinyl group, benzimidazolyl group, benzoxazolyl group,benzothiazolyl group, indazolyl group, benzisoxazolyl group,benzisothiazolyl group, dibenzofuranyl group, dibenzothiophenyl group,carbazolyl group, phenanthridinyl group, acridinyl group,phenanthrolinyl group, phenazinyl group, phenothiazinyl group,phenoxazinyl group and xanthenyl group, among which a furyl group,thienyl group, pyridyl group, pyridazynyl group, pyrimidinyl group,pyrazinyl group, triazinyl group, benzofuranyl group, benzothiophenylgroup, dibenzofuranyl group and dibenzothiophenyl group are preferable,and a benzofuranyl group, benzothiophenyl group, dibenzofuranyl groupand dibenzothiophenyl group are more preferable.

Any substituent in a “substituted or unsubstituted” compound representedby the formula (10) is preferably selected from the group consisting ofan alkyl group having 1 to 50 (preferably 1 to 10, more preferably 1 to5) carbon atoms, an alkenyl group having 2 to 20 (preferably 2 to 10)carbon atoms, an alkynyl group having 2 to 20 (preferably 2 to 10)carbon atoms, a cycloalkyl having 3 to 50 (preferably 3 to 6, morepreferably 5 or 6) ring carbon atoms, an aromatic hydrocarbon grouphaving 6 to 50 (preferably 6 to 24, more preferably 6 to 12) ring carbonatoms, an aralkyl group having 1 to 50 (preferably 1 to 10, morepreferably 1 to 5) carbon atoms containing an aromatic hydrocarbon grouphaving 6 to 50 (preferably 6 to 24, more preferably 6 to 12) ring carbonatoms, an amino group, a monoalkylamino or dialkylamino group having analkyl group having 1 to 50 (preferably 1 to 10, more preferably 1 to 5)carbon atoms, a monoarylamino or diarylamino group having an aromatichydrocarbon group having 6 to 50 (preferably 6 to 24, and morepreferably 6 to 12) ring carbon atoms, an alkoxy group having an alkylgroup having 1 to 50 (preferably 1 to 10, more preferably 1 to 5) carbonatoms, an aryloxy group having an aromatic hydrocarbon group having 6 to50 (preferably 6 to 24, and more preferably 6 to 12) ring carbon atoms,an alkylthio group having an alkyl group having 1 to 50 (preferably 1 to10, more preferably 1 to 5) carbon atoms, an arylthio group having anaromatic hydrocarbon group having 6 to 50 (preferably 6 to 24, and morepreferably 6 to 12) ring carbon atoms, a monosubstituted, disubstitutedor trisubstituted silyl group having a group selected from an alkylgroup having 1 to 50 (preferably 1 to 10, more preferably 1 to 5) carbonatoms and an aromatic hydrocarbon group having 6 to 50 (preferably 6 to24, more preferably 6 to 12) ring carbon atoms, a heterocyclic grouphaving 5 to 50 (preferably 5 to 24, more preferably 5 to 18) ring atomsand 1 to 5 (preferably 1 to 3, more preferably 1 or 2) hetero atoms(e.g., a nitrogen atom, oxygen atom and sulfur atom), a haloalkyl grouphaving 1 to 50 carbon atoms (preferably 1 to 10, and more preferably 1to 5 carbon atoms), a halogen atom (e.g., a fluorine atom, chlorineatom, bromine atom or iodine atom, preferably a fluorine atom), a cyanogroup, and a nitro group.

Among the above substituents, a substituent selected from the groupconsisting of an alkyl group having 1 to 5 carbon atoms, cycloalkylgroup having 5 or 6 carbon atoms, aromatic hydrocarbon group having 6 to12 ring carbon atoms, and heterocyclic group having 5 to 24 ring atomsand 1 to 3 hetero atoms (a nitrogen atom, oxygen atom and sulfur atom)is particularly preferable.

An alkyl group having 1 to 50 carbon atoms as a substituent in thesubstituted or unsubstituted group represents the same as thosedescribed as the alkyl group in Ar₁, Ar₂ and Ar₃.

An alkenyl group having 2 to 20 carbon atoms as a substituent in thesubstituted or unsubstituted group represents the same as thosedescribed as the alkenyl group in Ar_(t), Ar₂ and Ar₃.

An alkynyl group having 2 to 20 carbon atoms as a substituent in thesubstituted or unsubstituted group represents the same as thosedescribed as the alkynyl group in Ar₁, Ar₂ and Ar₃.

A cycloalkyl group having 3 to 50 ring carbon atoms as a substituent inthe substituted or unsubstituted group represents the same as thosedescribed as the cycloalkyl group in Ar₁, Ar₂ and Ar₃.

An aromatic hydrocarbon group having 6 to 50 ring carbon atoms as asubstituent in the substituted or unsubstituted group represents thesame as those described as the aromatic hydrocarbon group in Ar₁, Ar₂and Ar₃.

An aralkyl group having 6 to 50 ring carbon atoms as a substituent inthe substituted or unsubstituted group includes an aromatic hydrocarbongroup having 6 to 50 ring carbon atoms and an aralkyl group having 1 to50 carbon atoms. Examples of an alkyl group moiety are the same as theabove-described examples of the alkyl group. Examples of an aromatichydrocarbon group moiety are the same as the above-described examples ofthe aromatic hydrocarbon group.

In a monoalkylamino group or a dialkylamino group as a substituent inthe substituted or unsubstituted group, examples of an alkyl groupmoiety are the same as the above-described examples of the alkyl group.

In a monoarylamino group or a diarylamino group as a substituent in thesubstituted or unsubstituted group, examples of an aryl group (aromatichydrocarbon group) moiety are the same as the above-described examplesof the aromatic hydrocarbon group.

In an alkoxy group as a substituent in the substituted or unsubstitutedgroup, examples of an alkyl group moiety are the same as theabove-described examples of the alkyl group. For instance, the alkoxygroup is preferably a methoxy group and an ethoxy group.

In an aryloxy group as a substituent in the substituted or unsubstitutedgroup, examples of an aryl group (aromatic hydrocarbon group) moiety arethe same as the above-described examples of the aromatic hydrocarbongroup. The aryloxy group is exemplified by a phenoxy group.

In an alkylthio group as a substituent in the substituted orunsubstituted group, examples of an alkyl group moiety are the same asthe above-described examples of the alkyl group.

In an arylthio group as a substituent in the substituted orunsubstituted group, examples of an aryl group (aromatic hydrocarbongroup) moiety are the same as the above-described examples of thearomatic hydrocarbon group.

Examples of a mono-substituted silyl group, di-substituted silyl groupor trisubstituted silyl group as a substituent in the substituted orunsubstituted group include an alkylsilyl group having 1 to 50 carbonatoms and an arylsilyl group having 6 to 50 ring carbon atoms. Examplesof the alkylsilyl group having 1 to 50 carbon atoms include amonoalkylsilyl group, dialkylsilyl group and trialkylsilyl group.Specific examples of the alkyl group in each of those are the same asthe above-described examples of the alkyl group. Examples of thearylsilyl group having 6 to 50 ring carbon atoms include a monoarylsilylgroup, diarylsilyl group and triarylsilyl group. Specific examples ofeach aryl group in the arylsilyl group, which are the same aslater-described examples of the aryl group, include a trimethylsilylgroup, triethylsilyl group, t-butyldimethylsilyl group,vinyldimethylsilyl group, propyldimethylsilyl group,isopropyldimethylsilyl group, triphenylsilyl group, phenyldimethylsilylgroup, t-butyldiphenylsilyl group and tritolylsilyl group.

A heterocyclic group as a substituent in the substituted orunsubstituted group represents the same as those described as thearomatic heterocyclic group in Ar₁, Ar_(e) and Ar₃.

A haloalkyl group as a substituent in the substituted or unsubstitutedgroup is exemplified by a group obtained by halogenating theabove-described alkyl group, specifically, trifluoromethyl group.

Combination of First Compound and Second Compound

The organic EL device in the exemplary embodiment is capable ofprolonging a lifetime, improving a luminous efficiency, and inhibiting aroll-off when driven at a high current density. The roll-off refers to aphenomenon in which a luminous efficiency is decreased when the organicEL device is driven at a high current density.

The first compound contained in the emitting layer in the exemplaryembodiment is a delayed fluorescent compound. Since the delayedfluorescent compound has a donor (electron-donating) moiety and anacceptor (electron accepting) moiety in a molecular structure, electriccharges exist in a localized state in a molecule of the delayedfluorescent compound when the delayed fluorescent compound is excited.Since such a localized state of the electric charges possibly causesvarious side reactions, the delayed fluorescent compound having a longexcited lifetime tends to exhibit a low stability especially in theexcited state. Moreover, a half bandwidth of the luminescence spectrumof the delayed fluorescent compound is increased. Accordingly, it isdifficult to use the delayed fluorescent compound as a luminescentmaterial for a display unit requiring a high definition display in alarge-sized TV set and the like.

Accordingly, an organic EL device including an emitting layer containinga delayed fluorescent compound and a fluorescent compound has beenstudied. In the organic EL device with the above arrangement, thedelayed fluorescent compound is used as a sensitizer in the emittinglayer and the fluorescent compound is used as the luminescent material.According to the organic EL device with the above arrangement, since thefluorescent compound emits light, it is expected that the half bandwidthof the luminescence spectrum is decreased. Moreover, since emission fromthe delayed fluorescent compound having a low excitation stability canbe avoided, it is expected that a lifetime of the organic EL device isprolonged. Further, according to the organic EL device with thisarrangement, it is theoretically expected that the same luminousefficiency as that of an organic EL device including an emitting layercontaining a delayed fluorescent compound as a luminescent material isobtained.

The inventors have found that a combination of the delayed fluorescentcompound that is the first compound and the fluorescent compound that isthe second compound under predetermined conditions can provideadvantages of prolonging a lifetime, improving a luminous efficiency,and inhibiting a roll-off in a high current density region.

In the exemplary embodiment, an ionization potential Ip1 of the firstcompound and an ionization potential Ip2 of the second compoundpreferably satisfy a numerical formula below (Numerical Formula 1),further preferably satisfy a numerical formula below (Numerical Formula1A).0≤Ip2−Ip1≤0.8 eV  (Numerical Formula 1)0≤Ip2−Ip1≤0.8 eV  (Numerical Formula 1A)

When the numerical formula (Numerical Formula 1) is satisfied, aphenomenon (herein, also referred to as trap emission) in which holesentering the emitting layer are captured by the fluorescent secondcompound to emit light can be inhibited. When the trap emission isinhibited, a recombination of holes and electrons is promoted in thefirst compound that is the delayed fluorescent compound. Energy transferquickly occurs from the first compound in the excited state to thesecond compound, whereby the first compound is returned to the groundstate and the second compound is brought into the excited state. Whenthe second compound in the excited state is returned to the groundstate, the second compound emits light. As described above, it isdeduced that, since the recombination of holes and electrons in thefirst compound is promoted, excitons for contributing to emission fromthe second compound are increased, resulting in an improvement in theluminous efficiency.

Further, since the trap emission by the second compound is inhibited,carriers (holes and electrons) are inhibited from colliding againstexcitons (singlet excitons and triplet excitons). As a result, it isdeduced that, although the number of the carriers in the emitting layeris increased in the high current density region as compared with in thelow current density region, a roll-off in the high current densityregion is also inhibited because the organic EL device of the exemplaryembodiment can inhibit the carriers and the excitons from colliding tobe deactivated.

In the exemplary embodiment, Ip1 and Ip2 preferably satisfy a numericalformula below (Numerical Formula 2). When the numerical formula(Numerical Formula 2) is satisfied, the trap emission is easilyinhibitable.0≤Ip2−Ip1≤0.5 eV  (Numerical Formula 2)

It should be noted that, at Ip2−Ip1>0.8 eV, the electrons are capturedby the second compound to promote collision between the electrons andthe excitons, thereby promoting the roll-off. In the exemplaryembodiment, Ip1 and Ip2 more preferably satisfy a numerical formula(Numerical Formula 2A).0<Ip2−Ip1≤0.5 eV  (Numerical Formula 2A)

In the exemplary embodiment, since magnitude of the emission quantumefficiency of the first compound contributes to an energy transferefficiency, it is preferable that the emission quantum efficiency of thefirst compound is not excessively small, and is preferably 30% or more.On the other hand, when the emission quantum efficiency of the firstcompound exceeds 70%, the excited energy transfer

to the second compound and the emission process from the first compoundare likely to compete with each other. Accordingly, the emission quantumefficiency of the first compound is preferably 70% or less.

The organic EL device in the exemplary embodiment preferably emits lightexhibiting a peak in a wavelength range of 550 nm or less. In otherwords, the main peak wavelength of the light emitted from the organic ELdevice preferably falls within a range of 550 nm or less. When theorganic EL device in the exemplary embodiment emits light, it ispreferable that the second compound mainly emits light in the emittinglayer 5. The wavelength range of the light emitted by the organic ELdevice in the exemplary embodiment is more preferably from 430 nm to 550nm.

Moreover, it is also preferable that the organic EL device in theexemplary embodiment emits blue or green fluorescence.

TADF Mechanism

In the organic EL device of the exemplary embodiment, the first compoundis preferably a compound having a small ΔST(M1) so that inverseintersystem crossing from the triplet energy level of the first compoundto the singlet energy level thereof is easily caused by a heat energygiven from the outside. An energy state conversion mechanism to performspin exchange from the triplet state of electrically excited excitonswithin the organic EL device to the singlet state by inverse intersystemcrossing is referred to as a TADF mechanism.

FIG. 4 exemplarily shows a relationship in energy levels between thefirst compound and the second compound in the emitting layer. In FIG. 4,S0 represents a ground state, S1(M1) represents a lowest singlet stateof the first compound, T1(M1) represents a lowest triplet state of thefirst compound, S1(M2) represents a lowest singlet state of the secondcompound, and T1(M2) represents a lowest triplet state of the secondcompound. A dashed arrow directed from S1(M1) to S1(M2) in FIG. 4represents Förster energy transfer from the lowest singlet state of thefirst compound to the lowest singlet state of the second compound. Adifference between the lowest singlet state S1 and the lowest tripletstate T1 is defined as ΔST.

As shown in FIG. 4, when a compound having a small ΔST(M1) is used asthe first compound, inverse intersystem crossing from the lowest tripletstate T1(M1) to the lowest singlet state S1(M1) can be caused by a heatenergy. Accordingly, Förster energy transfer from the lowest singletstate S1 (M1) of the first compound to the lowest singlet state S1(M2)of the second compound is caused. As a result, fluorescence from thelowest singlet state S1(M2) of the second compound can be observed. Itis considered that the internal quantum efficiency can be theoreticallyraised up to 100% also by using delayed fluorescence by the TADFmechanism.

In the exemplary embodiment, a singlet energy S(M1) of the firstcompound is preferably larger than a singlet energy S(M2) of the secondcompound.

In the exemplary embodiment, an energy gap T_(77K)(M1) at 77[K] of thefirst compound is preferably larger than an energy gap T_(77K)(M2) at77[K] of the second compound. T_(77K)(M1) is preferably 2.0 eV or more,more preferably 2.2 eV or more.

Relationship Between Triplet Energy and Energy Gap at 77 [K]

Description will be made on a relationship between a triplet energy andan energy gap at 77 [K]. In the exemplary embodiment, the energy gap at77 [K] is different from a typical triplet energy in some aspects.

The triplet energy is measured as follows. Firstly, a target compoundfor measurement is deposited on a quartz substrate to prepare a sample.Alternatively, the target compound is dissolved in an appropriatesolvent to prepare a solution and the solution is encapsulated in aquartz glass pipe to prepare a sample. A phosphorescent spectrum(ordinate axis: phosphorescent luminous intensity, abscissa axis:wavelength) of the sample is measured at a low temperature (77K). Atangent is drawn to the rise of the phosphorescent spectrum on theshort-wavelength side. The triplet energy is calculated by apredetermined conversion equation based on a wavelength value at anintersection of the tangent and the abscissa axis.

The first compound usable in the exemplary embodiment is preferably acompound having a small ΔST. When ΔST is small, intersystem crossing andinverse intersystem crossing are likely to occur even at a lowtemperature (77K), so that the singlet state and the triplet statecoexist. As a result, the spectrum to be measured in the same manner asthe above includes emission from both the singlet state and the tripletstate. Although it is difficult to distinguish the emission from thesinglet state from the emission from the triplet state, the value of thetriplet energy is basically considered dominant.

Accordingly, in the exemplary embodiment, the triplet energy is measuredby the same method as a typical triplet energy T, but a value measuredin the following manner is referred to as an energy gap T_(77K) in orderto differentiate the measured energy from the typical triplet energy ina strict meaning. In the measurement using a thin film, the targetcompound for the measurement is deposited at a film thickness of 100 nmon a quartz substrate to form a sample. A phosphorescent spectrum(ordinate axis: phosphorescent luminous intensity, abscissa axis:wavelength) of the sample is measured at a low temperature (77K). Atangent is drawn to the rise of the phosphorescent spectrum on theshort-wavelength side. An energy amount is calculated by the followingconversion equation 1 based on a wavelength value λ_(edge) [nm] at anintersection of the tangent and the abscissa axis and defined as anenergy gap T_(77K).T _(77K)[eV]=1239.85/λ_(dge)  Conversion Equation 1:

The tangent to the rise of the phosphorescence spectrum on theshort-wavelength side is drawn as follows. While moving on a curve ofthe phosphorescence spectrum from the short-wavelength side to themaximum spectral value closest to the short-wavelength side among themaximum spectral values, a tangent is checked at each point on the curvetoward the long-wavelength of the phosphorescence spectrum. Aninclination of the tangent is increased as the curve rises (i.e., avalue of the ordinate axis is increased). A tangent drawn at a point ofthe maximum inclination (i.e., a tangent at an inflection point) wasdefined as the tangent to the rise of the phosphorescence spectrum onthe short-wavelength side.

The maximum with peak intensity being 15% or less of the maximum peakintensity of the spectrum is not included in the above-mentioned maximumclosest to the short-wavelength side of the spectrum. The tangent drawnat a point of the maximum spectral value being closest to theshort-wavelength side and having the maximum inclination is defined as atangent to the rise of the phosphorescence spectrum on theshort-wavelength side.

For phosphorescence measurement, a spectrophotofluorometer body F-4500(manufactured by Hitachi High-Technologies Corporation) is usable. Themeasurement instrument is not limited to this arrangement. A combinationof a cooling unit, a low temperature container, an excitation lightsource and a light-receiving unit may be used for measurement.

Singlet Energy S

The singlet energy S is measured as follows.

10 μmol/L of a toluene solution containing the target compound for themeasurement was prepared and put in a quartz cell to prepare a sample.An absorption spectrum (ordinate axis: luminous intensity, abscissaaxis: wavelength) of the sample was measured at a normal temperature(300K). A tangent was drawn to the fall of the absorption spectrum onthe long-wavelength side, and a wavelength value λ_(edge) [nm] at anintersection of the tangent and the abscissa axis was substituted in thefollowing conversion equation to calculate a singlet energy.S[eV]=1239.85/λ_(edge)  Conversion Equation 2:

In Example, the absorption spectrum was measured using aspectrophotometer manufactured by Hitachi, Ltd. (device name: U3310). Itshould be noted that the absorption spectrum measuring device may bedifferent from the above device.

The tangent to the fall of the absorption spectrum on thelong-wavelength side is drawn as follows. While moving on a curve of theabsorption spectrum from the maximum spectral value closest to thelong-wavelength side in a long-wavelength direction, a tangent at eachpoint on the curve is checked. An inclination of the tangent isdecreased and increased in a repeated manner as the curve falls (i.e., avalue of the ordinate axis is decreased). A tangent drawn at a point ofthe minimum inclination closest to the long-wavelength side (except whenabsorbance is 0.1 or less) is defined as the tangent to the fall of theabsorption spectrum on the long-wavelength side.

The maximum absorbance of 0.2 or less is not included in theabove-mentioned maximum absorbance on the long-wavelength side.

Film Thickness of Emitting Layer

A film thickness of the emitting layer 5 of the organic EL device 1 ofthe exemplary embodiment is preferably in a range from 5 nm to 100 nm,more preferably in a range from 7 nm to 100 nm, and most preferably in arange from 10 nm to 100 nm. The thickness of less than 5 nm may causedifficulty in forming the emitting layer 5 and in controllingchromaticity, while the thickness of more than 100 nm may raise drivevoltage.

Content Ratio of Compounds in Emitting Layer

In the emitting layer 5 of the organic EL device 1 according to theexemplary embodiment, a content ratio of the first compound ispreferably 5 mass % or more, more preferably in a range from 10 mass %to 80 mass %, further preferably in a range from 40 mass % to 60 mass %.A content ratio of the second compound is preferably in a range from 1mass % to 10 mass %. An upper limit of the total of the respectivecontent ratios of the first and second compounds in the emitting layer 5is 100 mass %. It should be noted that the emitting layer 5 of theexemplary embodiment may further contain another material in addition tothe first and second compounds.

Substrate

A substrate 2 is used as a support for the organic EL device 1. Forinstance, glass, quartz, plastics and the like are usable as thesubstrate 2. A flexible substrate is also usable. The flexible substrateis a bendable substrate. The flexible substrate is exemplified by aplastic substrate formed of polycarbonate, polyarylate,polyethersulfone, polypropylene, polyester, polyvinyl fluoride,polyvinyl chloride, polyimide, polyethylene naphthalate or the like.Moreover, an inorganic vapor deposition film is also usable as thesubstrate 2.

Anode

Metal, alloy, an electrically conductive compound, a mixture thereof andthe like, which have a large work function (specifically, of 4.0 eV ormore) is preferably usable as the anode 3 formed on the substrate 2.Specific examples of the material for the anode include indium tin oxide(ITO), indium tin oxide containing silicon or silicon oxide, indium zincoxide, tungsten oxide, indium oxide containing zinc oxide and graphene.In addition, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chrome(Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium(Pd), titanium (Ti), or nitrides of a metal material (e.g., titaniumnitride) are usable.

The above materials are typically deposited as a film by sputtering. Forinstance, indium zinc oxide can be deposited as a film by sputteringusing a target that is obtained by adding zinc oxide in a range from 1mass % to 10 mass % to indium oxide. Moreover, for instance, indiumoxide containing tungsten oxide and zinc oxide can be deposited as afilm by sputtering using a target that is obtained by adding tungstenoxide in a range from 0.5 mass % to 5 mass % and zinc oxide in a rangefrom 0.1 mass % to 1 mass % to indium oxide. In addition, vapordeposition, coating, ink jet printing, spin coating and the like may beused for forming the anode 3.

Among the organic layers formed on the anode 3, a hole injecting layer 6formed adjacent to the anode 3 is formed of a composite material thatfacilitates injection of holes irrespective of the work function of theanode 3. Accordingly, a material usable as an electrode material (e.g.,metal, alloy, an electrically conductive compound, a mixture thereof,and elements belonging to Groups 1 and 2 of the periodic table of theelements) is usable as the material for the anode 3.

The elements belonging to Groups 1 and 2 of the periodic table of theelements, which are materials having a small work function, namely, analkali metal such as lithium (Li) and cesium (Cs) and an alkaline earthmetal such as magnesium (Mg), calcium (Ca) and strontium (Sr), alloythereof (e.g., MgAg, AlLi), a rare earth metal such as europium (Eu) andytterbium (Yb), and alloy thereof are also usable as the material forthe anode. When the anode 3 is formed of the alkali metal, alkalineearth metal and alloy thereof, vapor deposition and sputtering areusable. Further, when the anode 3 is formed of silver paste and thelike, coating, ink jet printing and the like are usable.

Hole Injecting Layer

A hole injecting layer 6 is a layer containing a highly hole-injectablesubstance. Examples of the highly hole-injectable substance includemolybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide,ruthenium oxide, chromium oxide, zirconium oxide, hafnium oxide,tantalum oxide, silver oxide, tungsten oxide, and manganese oxide.

In addition, the examples of the highly hole-injectable substancefurther include: an aromatic amine compound, which is a low-moleculecompound, such that 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation:DPAB),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B),3-[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazole-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2), and3-[N-(1-naphthyl)-N-(9-phenylcarbazole-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1); anddipyrazino[2,3-f:20,30-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile(HAT-CN).

Moreover, a high-molecule compound (e.g., an oligomer, dendrimer andpolymer) is also usable as the highly hole-injectable substance.Examples of the high-molecule compound include poly(N-vinylcarbazole)(abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamido](abbreviation: PTPDMA), andpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:Poly-TPD). Furthermore, the examples of the high-molecule compoundinclude a high-molecule compound added with an acid such aspoly(3,4-ethylene dioxythiophene)/poly(styrene sulfonic acid)(PEDOT/PSS), and polyaniline/poly(styrene sulfonic acid) (PAni/PSS).

Hole Transporting Layer

A hole transporting layer 7 is a layer containing a highlyhole-transportable substance. An aromatic amine compound, carbazolederivative, anthracene derivative and the like are usable for the holetransporting layer 7. Specific examples of a material for the holetransporting layer 7 include4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4-phenyl-4′-(9-phenylfluorene-9-yl)triphenylamine(abbreviation: BAFLP),4,4′-bis[N-(9,9-dimethylfluorene-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi), 4,4′,4″-tris(N,N-diphenylamino)triphenyl amine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), and4,4′-bis[N-(spiro-9,9′-bifluorene-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). The above-described substances mostly have a holemobility of 10⁻⁶ cm²/(V·s) or more.

A carbazole derivative such as CBP, 9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene (CzPA) and9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (PCzPA); ananthracene derivative such as t-BuDNA, DNA, and DPAnth; and ahigh-molecular weight compound such aspoly(N-vinylcarbazole)(abbreviation: PVK) andpoly(4-vinyltriphenylamine)(abbreviation: PVTPA) are usable for the holetransporting layer 7.

However, any substance having a hole transporting performance higherthan an electron transporting performance may be used in addition to theabove substances. A highly hole-transportable substance may be providedin the form of a single layer or a laminated layer of two or more layersof the above substance.

When the hole transporting layer includes two or more layers, one of thelayers with a larger energy gap is preferably provided closer to theemitting layer 5.

In the exemplary embodiment, the hole transporting layer 7 preferablyhas a function of preventing triplet excitons generated in the emittinglayer 5 from diffusing into the hole transporting layer to trap thetriplet excitons within the emitting layer 5.

Electron Transporting Layer

An electron transporting layer 8 is a layer containing a highlyelectron-transportable substance. As the electron transporting layer, 1)a metal complex such as an aluminum complex, beryllium complex and zinccomplex, 2) heteroaromatic compound such as an imidazole derivative,benzimidazole derivative, azine derivative, carbazole derivative, andphenanthroline derivative, and 3) a high-molecule compound are usable.Specifically, as a low-molecule organic compound, a metal complex suchas Alq, tris(4-methyl-8-quinolinato)aluminum (abbreviation: Almq3),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq2), BAlq,Znq, ZnPBO and ZnBTZ are usable. In addition to the metal complex, aheteroaromatic compound such as2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(ptert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene(abbreviation: OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), and4,4′-bis(5-methylbenzoxazole-2-yl)stilbene (abbreviation: BzOs) areusable. In the exemplary embodiment, a benzimidazole compound issuitably usable. The above-described substances mostly have an electronmobility of 10⁻⁶ cm²/(V·s) or more. However, any substance having anelectron transporting performance higher than a hole transportingperformance may be used for the electron transporting layer 8 inaddition to the above substances. The electron transporting layer 8 maybe provided in the form of a single layer or a laminated layer of two ormore layers of the above substance(s).

Moreover, a high-molecule compound is also usable for the electrontransporting layer 8. For instance,poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py),poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation:PF-BPy) and the like are usable.

In the exemplary embodiment, the hole transporting layer 8 preferablyhas a function of preventing triplet excitons generated in the emittinglayer 5 from diffusing into the hole transporting layer 8 and theelectron injecting layer 9 to trap the triplet excitons within theemitting layer 5.

Electron Injecting Layer

An electron injecting layer 9 is a layer containing a highlyelectron-injectable substance. Examples of a material for the electroninjecting layer include an alkali metal, alkaline earth metal and acompound thereof, examples of which include lithium (Li), cesium (Cs),calcium (Ca), lithium fluoride (LiF), cesium fluoride (CsF), calciumfluoride (CaF2), and lithium oxide (LiOx). In addition, a substanceobtained by containing an alkali metal, alkaline earth metal or acompound thereof in the electron transportable substance, specifically,for instance, a substance obtained by containing magnesium (Mg) in Alqmay be used. With this substance, electrons can be more efficientlyinjected from the cathode 4.

Alternatively, a composite material provided by mixing an organiccompound with an electron donor may be used for the electron injectinglayer 9. The composite material exhibits excellent electron injectingperformance and electron transporting performance since the electrondonor generates electron in the organic compound. In this arrangement,the organic compound is preferably a material exhibiting an excellenttransforming performance of the generated electrons. Specifically, forinstance, the above-described substance for the electron transportinglayer 8 (e.g., the metal complex and heteroaromatic compound) is usable.The electron donor may be any substance exhibiting an electron donatingperformance to the organic compound. Specifically, an alkali metal,alkaline earth metal and a rare earth metal are preferable, examples ofwhich include lithium, cesium, magnesium, calcium, erbium and ytterbium.Moreover, an alkali metal oxide and alkaline earth metal oxide arepreferable, examples of which include lithium oxide, calcium oxide, andbarium oxide. Further, Lewis base such as magnesium oxide is alsousable. Furthermore, tetrathiafulvalene (abbreviation: TTF) is alsousable.

Cathode

Metal, alloy, an electrically conductive compound, a mixture thereof andthe like, which have a small work function, specifically, of 3.8 eV orless, is preferably usable as a material for the cathode 4. Specificexamples of the material for the cathode 4 include: the elementsbelonging to Groups 1 and 2 of the periodic table of the elements,namely, an alkali metal such as lithium (Li) and cesium (Cs) and analkaline earth metal such as magnesium (Mg), calcium (Ca) and strontium(Sr); alloy thereof (e.g., MgAg, AlLi); a rare earth metal such aseuropium (Eu) and ytterbium (Yb); and alloy thereof.

When the cathode 4 is formed of the alkali metal, alkaline earth metaland alloy thereof, vapor deposition and sputtering are usable. Moreover,when the cathode 4 is formed of silver paste and the like, coating, inkjet printing and the like are usable.

By providing the electron injecting layer 9, various conductivematerials such as Al, Ag, ITO, graphene and indium tin oxide containingsilicon or silicon oxide are usable for forming the cathode 4irrespective of the magnitude of the work function. The conductivematerials can be deposited as a film by sputtering, ink jet printing,spin coating and the like.

Layer Formation Method(s)

There is no restriction except for the above particular description fora method for forming each layer of the organic EL device 1 in theexemplary embodiment. Known methods such as dry film-forming and wetfilm-forming are applicable. Examples of the dry film-forming includevacuum deposition, sputtering, plasma and ion plating. Examples of thewet film-forming include spin coating, dipping, flow coating and ink jetprinting.

Film Thickness

There is no restriction except for the above particular description fora film thickness of each of the organic layers of the organic EL device1 in the exemplary embodiment. The film thickness is typicallypreferably in a range of several nanometers to 1 μm because anexcessively-thinned film is likely to cause defects such as a pin holewhile an excessively-thickened film requires high voltage to be appliedand deteriorates efficiency.

Herein, the number of carbon atoms forming a ring (also referred to asring carbon atoms) means the number of carbon atoms included in atomsforming the ring itself of a compound in which the atoms are bonded toform the ring (e.g., a monocyclic compound, a fused ring compound, across-linked compound, a carbocyclic compound, and a heterocycliccompound). When the ring is substituted by a substituent, the “ringcarbon atoms” do not include carbon(s) contained in the substituent.Unless specifically described, the same applies to the “ring carbonatoms” described later. For instance, a benzene ring has 6 ring carbonatoms, a naphthalene ring has 10 ring carbon atoms, a pyridinyl grouphas 5 ring carbon atoms, and a furanyl group has 4 ring carbon atoms.When the benzene ring and/or the naphthalene ring is substituted by, forinstance, an alkyl group, the number of carbon atoms of the alkyl groupis not included in the number of the ring carbon atoms. When a fluorenering is substituted by, for instance, a fluorene ring (e.g., aspirofluorene ring), the number of carbon atoms of the fluorene ring asa substituent is not counted in the number of the ring carbon atoms forthe fluorene ring.

Herein, the number of atoms forming a ring (also referred to as ringatoms) means the number of atoms forming the ring itself of a compoundin which the atoms are bonded to form the ring (e.g., a monocycliccompound, a fused ring compound, a cross-linked compound, a carbocycliccompound, and a heterocyclic compound). Atom(s) not forming the ring(e.g., a hydrogen atom for terminating the atoms forming the ring) andatoms included in a substituent substituting the ring are not counted inthe number of the ring atoms. Unless specifically described, the sameapplies to the “ring atoms” described later. For instance, a pyridinering has 6 ring atoms, a quinazoline ring has 10 ring atoms, and a furanring has 5 ring atoms. Hydrogen atoms respectively bonded to thepyridine ring and the quinazoline ring and atoms forming thesubstituents are not counted in the number of the ring atoms. When afluorene ring is substituted by, for instance, a fluorene ring (e.g., aspirofluorene ring), the number of atoms of the fluorene ring as asubstituent is not included in the number of the ring atoms for thefluorene ring.

Next, each of substituents described in the above formulae will bedescribed.

Examples of the aromatic hydrocarbon group (occasionally referred to asan aryl group) having 6 to 30 ring carbon atoms or 6 to 40 ring carbonatoms herein include a phenyl group, biphenyl group, terphenyl group,naphthyl group, anthryl group, phenanthryl group, fluorenyl group,pyrenyl group, chrysenyl group, fluoranthenyl group, benz[a]anthrylgroup, benzo[c]phenanthryl group, triphenylenyl group,benzo[k]fluoranthenyl group, benzo[g]chrysenyl group,benzo[b]triphenylenyl group, picenyl group, and perylenyl group.

The aryl group herein preferably has 6 to 20 ring carbon atoms, morepreferably 6 to 14 ring carbon atoms, further preferably 6 to 12 ringcarbon atoms. Among the aryl group, a phenyl group, biphenyl group,naphthyl group, phenanthryl group, terphenyl group and fluorenyl groupare particularly preferable. A carbon atom at a position 9 of each of1-fluorenyl group, 2-fluorenyl group, 3-fluorenyl group and 4-fluorenylgroup is preferably substituted by a substituted or unsubstituted alkylgroup having 1 to 30 carbon atoms or a substituted or unsubstituted arylgroup having 6 to 18 ring carbon atoms later described herein.

The heterocyclic group (occasionally, referred to as heteroaryl group,heteroaromatic ring group or aromatic heterocyclic group) having 5 to 30ring atoms herein preferably contains at least one atom selected fromthe group consisting of nitrogen, sulfur, oxygen, silicon, selenium atomand germanium atom, and more preferably contains at least one atomselected from the group consisting of nitrogen, sulfur and oxygen.

Examples of the heterocyclic group (occasionally, referred to asheteroaryl group, heteroaromatic ring group or aromatic heterocyclicgroup) having 5 to 30 ring atoms herein include a pyridyl group,pyrimidinyl group, pyrazinyl group, pyridazynyl group, triazinyl group,quinolyl group, isoquinolinyl group, naphthyridinyl group, phthalazinylgroup, quinoxalinyl group, quinazolinyl group, phenanthridinyl group,acridinyl group, phenanthrolinyl group, pyrrolyl group, imidazolylgroup, pyrazolyl group, triazolyl group, tetrazolyl group, indolylgroup, benzimidazolyl group, indazolyl group, imidazopyridinyl group,benzotriazolyl group, carbazolyl group, furyl group, thienyl group,oxazolyl group, thiazolyl group, isoxazolyl group, isothiazolyl group,oxadiazolyl group, thiadiazolyl group, benzofuranyl group,benzothiophenyl group, benzoxazolyl group, benzothiazolyl group,benzisoxazolyl group, benzisothiazolyl group, benzoxadiazolyl group,benzothiadiazolyl group, dibenzofuranyl group, dibenzothiophenyl group,piperidinyl group, pyrrolidinyl group, piperazinyl group, morpholylgroup, phenazinyl group, phenothiazinyl group, and phenoxazinyl group.

The heterocyclic group herein preferably has 5 to 20 ring atoms, morepreferably 5 to 14 ring atoms. Among the above, a 1-dibenzofuranylgroup, 2-dibenzofuranyl group, 3-dibenzofuranyl group, 4-dibenzofuranylgroup, 1-dibenzothiophenyl group, 2-dibenzothiophenyl group,3-dibenzothiophenyl group, 4-dibenzothiophenyl group, 1-carbazolylgroup, 2-carbazolyl group, 3-carbazolyl group, 4-carbazolyl group, and9-carbazolyl group are particularly preferable. A nitrogen atom at aposition 9 of each of 1-carbazolyl group, 2-carbazolyl group,3-carbazolyl group and 4-carbazolyl group is preferably substituted by asubstituted or unsubstituted aryl group having 6 to 30 ring carbon atomsor a substituted or unsubstituted heterocyclic group having 5 to 30 ringatoms herein.

Herein, the heterocyclic group may be a group derived from any one ofpartial structures represented by formulae (XY-1) to (XY-18).

In the formulae (XY-1) to (XY-18), X and Y each independently representa hetero atom, and preferably represent an oxygen atom, sulfur atom,selenium atom, silicon atom or germanium atom. The partial structuresrepresented by the formulae (XY-1) to (XY-18) may each be bonded in anyposition to be a heterocyclic group, which may be substituted.

Herein, examples of the substituted or unsubstituted carbazolyl groupmay include a group in which a carbazole ring is further fused with aring(s) as shown in the following formulae. Such a group may besubstituted. The group may be bonded in any position as desired.

The alkyl group having 1 to 30 carbon atoms herein may be linear,branched or cyclic. Examples of the linear or branched alkyl group are amethyl group, ethyl group, propyl group, isopropyl group, n-butyl group,s-butyl group, isobutyl group, t-butyl group, n-pentyl group, n-hexylgroup, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group,n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group,n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecylgroup, neo-pentyl group, amyl group, isoamyl group, 1-methylpentylgroup, 2-methylpentyl group, 1-pentylhexyl group, 1-butylpentyl group,1-heptyloctyl group and 3-methylpentyl group.

The linear or branched alkyl group herein preferably has 1 to 10 carbonatoms, more preferably 1 to 6 carbon atoms. Among the linear or branchedalkyl group, a methyl group, ethyl group, propyl group, isopropyl group,n-butyl group, s-butyl group, isobutyl group, t-butyl group, n-pentylgroup, n-hexyl group, amyl group, isoamyl group and neopentyl group areparticularly preferable.

Examples of the cycloalkyl group having 3 to 30 carbon atoms herein area cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexylgroup, 4-methylcyclohexyl group, adamantyl group and norbornyl group.The cycloalkyl group preferably has 3 to 10 ring carbon atoms, morepreferably 5 to 8 ring carbon atoms. Among the cycloalkyl group, acyclopentyl group and a cyclohexyl group are particularly preferable.

A halogenated alkyl group provided by substituting an alkyl group with ahalogen atom is exemplified by one provided by substituting an alkylgroup having 1 to 30 carbon atoms with one or more halogen groups.Specific examples of the above halogenated alkyl group are afluoromethyl group, difluoromethyl group, trifluoromethyl group,fluoroethyl group, trifluoromethylmethyl group, trifluoroethyl group andpentafluoroethyl group.

Herein, “carbon atoms forming a ring (ring carbon atoms)” mean carbonatoms forming a saturated ring, unsaturated ring, or aromatic ring.“Atoms forming a ring (ring atoms)” mean carbon atoms and hetero atomsforming a hetero ring including a saturated ring, unsaturated ring, oraromatic ring.

Herein, a “hydrogen atom” means isotopes having different neutronnumbers and specifically encompasses protium, deuterium and tritium.

Herein, in addition to the above-described aryl group, heterocyclicgroup, alkyl group (linear or branched alkyl group, cycloalkyl group andhaloalkyl group), examples of the substituent meant by “substituted orunsubstituted” include an aralkyl group, substituted amino group,halogen atom, cyano group, alkoxy group, aryloxy group, alkylsilylgroup, arylsilyl group, alkenyl group, alkynyl group, alkylthio group,arylthio group, hydroxyl group, nitro group, and carboxy group.

Among the above substituents, an aryl group, heterocyclic group, alkylgroup, halogen atom, alkylsilyl group, arylsilyl group and cyano groupare preferable. More preferable substituents are one listed as thepreferable substituents described for each substituent.

The above substituents may be further substituted by at least one groupselected from the group consisting of an aryl group, heterocyclic group,alkyl group, alkylsilyl group, arylsilyl group, alkoxy group, aryloxygroup, alkylamino group, arylamino group, alkylthio group, arylthiogroup, alkenyl group, alkynyl group, aralkyl group, halogen atom, cyanogroup, hydroxyl group, nitro group, and carboxy group. In addition,plural ones of these substituents may be mutually bonded to form a ring.

The alkoxy group having 1 to 30 carbon atoms is represented by —OZ₁. Z₁is exemplified by the above alkyl group having 1 to 30 carbon atoms.Examples of the alkoxy group are a methoxy group, ethoxy group, propoxygroup, butoxy group, pentyloxy group and hexyloxy group. The alkoxygroup preferably has 1 to 20 carbon atoms.

A halogenated alkoxy group provided by substituting an alkoxy group witha halogen atom is exemplified by one provided by substituting an alkoxygroup having 1 to 30 carbon atoms with one or more halogen groups.

The aryloxy group having 6 to 30 ring carbon atoms is represented by—OZ₂. Z₂ is exemplified by the above aryl group having 6 to 30 ringcarbon atoms. The aryloxy group preferably has 6 to 20 ring carbonatoms. The aryloxy group is exemplified by a phenoxy group.

Examples of the substituted amino group include an alkylamino grouphaving 2 to 30 carbon atoms and an arylamino group having 6 to 60 ringcarbon atoms.

The alkylamino group having 2 to 30 carbon atoms is represented by—NHR_(V) or —N(R_(V))₂. R_(V) is exemplified by the alkyl group having 1to 30 carbon atoms.

The arylamino group having 6 to 60 ring carbon atoms is represented by—NHR_(W) or —N(R_(W))₂. R_(W) is exemplified by the above aryl grouphaving 6 to 30 ring carbon atoms.

Examples of the halogen atom include a fluorine atom, chlorine atom,bromine torn and iodine atom, among which a fluorine atom is preferable.

The aralkyl group is preferably an aralkyl group having 6 to 30 ringcarbon atoms and is represented by —Z₃-Z₄. Z₃ is exemplified by analkylene group corresponding to the above alkyl group having 1 to 30carbon atoms. Z₄ is exemplified by the above aryl group having 6 to 30ring carbon atoms. This aralkyl group is preferably an aralkyl grouphaving 7 to 30 carbon atoms, in which an aryl moiety has 6 to 30 carbonatoms, preferably 6 to 20 carbon atoms, more preferably 6 to 12 carbonatoms and an alkyl moiety has 1 to 30 carbon atoms, preferably 1 to 20carbon atoms, more preferably 1 to 10 carbon atoms, further preferably 1to 6 carbon atoms. Examples of the aralkyl group include a benzyl group,2-phenylpropane-2-yl group, 1-phenylethyl group, 2-phenylethyl group,1-phenylisopropyl group, 2-phenylisopropyl group, phenyl-t-butyl group,α-naphthylmethyl group, 1-α-naphthylethyl group, 2-α-naphthylethylgroup, 1-α-naphthylisopropyl group, 2-α-naphthylisopropyl group,β-naphthylmethyl group, 1-β-naphthylethyl group, 2-β-naphthylethylgroup, 1-β-naphthylisopropyl group, and 2-β-naphthylisopropyl group.

The alkenyl group is preferably an alkenyl group having 2 to 30 carbonatoms, which may be linear, branched or cyclic. Examples of the alkenylgroup include a vinyl group, propenyl group, butenyl group, oleyl group,eicosapentaenyl group, docosahexaenyl group, styryl group,2,2-diphenylvinyl group, 1,2,2-triphenylvinyl group, 2-phenyl-2-propenylgroup, cyclopentadienyl group, cyclopentenyl group, cyclohexenyl group,and cyclohexadienyl group.

The alkynyl group is preferably an alkynyl group having 2 to 30 carbonatoms, which may be linear, branched or cyclic. Examples of the alkynylgroup include ethynyl, propynyl, and 2-phenylethynyl.

The alkylthio group having 1 to 30 carbon atoms is represented by—SR_(V). R_(V) is exemplified by the alkyl group having 1 to 30 carbonatoms. The alkylthio group preferably has 1 to 20 carbon atoms.

The arylthio group having 6 to 30 ring carbon atoms is represented by—SR_(W). R_(W) is exemplified by the above aryl group having 6 to 30ring carbon atoms. The arylthio group preferably has 6 to 20 ring carbonatoms.

Examples of the substituted silyl group include an alkylsilyl grouphaving 3 to 30 carbon atoms and an arylsilyl group having 6 to 30 ringcarbon atoms.

The alkylsilyl group having 3 to 30 carbon atoms herein is exemplifiedby an alkylsilyl group having the alkyl group listed as the examples ofthe alkyl group having 1 to 30 carbon atoms. Specifically, examples ofthe alkylsilyl group are a trimethylsilyl group, a triethylsilyl group,a tri-n-butylsilyl group, a tri-n-octylsilyl group, a triisobutylsilylgroup, a dimethylethylsilyl group, a dimethylisopropylsilyl group, adimethyl-n-propylsilyl group, a dimethyl-n-butylsilyl group, adimethyl-t-butylsilyl group, a diethylisopropylsilyl group, avinyldimethylsilyl group, a propyldimethylsilyl group andtriisopropylsilyl group. Three alkyl groups in the trialkylsilyl groupmay be the same or different.

Examples of the arylsilyl group having 6 to 30 ring carbon atoms are adialkylarylsilyl group, alkyldiarylsilyl group and triarylsilyl group.

The dialkylarylsilyl group is exemplified by a dialkylarylsilyl groupincluding two of the alkyl group listed as the examples of the alkylgroup having 1 to 30 carbon atoms and one of the aryl group listed asthe examples of the aryl group having 6 to 30 ring carbon atoms. Thedialkylarylsilyl group preferably has 8 to 30 carbon atoms.

The alkyldiarylsilyl group is exemplified by an alkyldiarylsilyl groupincluding one of the alkyl group listed as the examples of the alkylgroup having 1 to 30 carbon atoms and two of the aryl group listed asthe examples of the aryl group having 6 to 30 ring carbon atoms. Thealkyldiarylsilyl group preferably has 13 to 30 carbon atoms.

The triarylsilyl group is exemplified by a triarylsilyl group includingthree of the aryl group listed as the examples of the aryl group having6 to 30 ring carbon atoms. The triarylsilyl group preferably has 18 to30 carbon atoms.

An aldehyde group, carbonyl group, ester group, carbamoyl group, andamino group may be substituted by an aliphatic hydrocarbon, alicyclichydrocarbon, aromatic hydrocarbon, or heterocycle. The aliphatichydrocarbon, alicyclic hydrocarbon, aromatic hydrocarbon, andheterocycle may further have a substituent. A siloxanyl group is asilicon compound group with an ether bond and is exemplified by atrimethylsiloxanyl group.

“Unsubstituted” in “substituted or unsubstituted” herein means that agroup is not substituted by the above-described substituents but bondedwith a hydrogen atom.

Herein, “XX to YY carbon atoms” in the description of “substituted orunsubstituted ZZ group having XX to YY carbon atoms” represent carbonatoms of an unsubstituted ZZ group and do not include carbon atoms of asubstituent(s) of the substituted ZZ group. Herein, “YY” is larger than“XX.” “XX” and “YY” each mean an integer of 1 or more.

Herein, “XX to YY atoms” in the description of “substituted orunsubstituted ZZ group having XX to YY atoms” represent atoms of anunsubstituted ZZ group and does not include atoms of a substituent(s) ofthe substituted ZZ group. Herein, “YY” is larger than “XX.” “XX” and“YY” each mean an integer of 1 or more.

Herein, when the substituents are mutually bonded to form a ringstructure, the ring structure is a saturated ring, unsaturated ring,aromatic hydrocarbon ring, or a heterocycle. In addition, the ringstructure formed by bonding the substituents may have a substituent.

Herein, examples of the aromatic hydrocarbon group and the heterocyclicgroup in the linking group include divalent groups obtained byeliminating one hydrogen atom from the above monovalent groups.

Moreover, herein, examples of the aromatic hydrocarbon ring and theheterocycle include ring structures from which the above monovalentgroups are derived.

Electronic Device

The organic EL device 1 according to the exemplary embodiment of theinvention is usable in an electronic device such as a display unit and alight-emitting unit. Examples of the display unit include displaycomponents such as an organic EL panel module, TV, mobile phone, tablet,and personal computer. Examples of the light-emitting unit include anilluminator and a vehicle light.

Second Exemplary Embodiment

Arrangement(s) of an organic EL device according to a second exemplaryembodiment will be described below. In the description of the secondexemplary embodiment, the same components as those in the firstexemplary embodiment are denoted by the same reference signs and namesto simplify or omit an explanation of the components. In the secondexemplary embodiment, the same materials and compounds as described inthe first exemplary embodiment are usable for a material and a compoundwhich are not particularly described.

The organic EL device according to the second exemplary embodiment isdifferent from the organic EL device according to the first exemplaryembodiment in that the emitting layer further includes a third compound.Other components are the same as those in the first exemplaryembodiment.

Third Compound

A singlet energy of the third compound is larger than the singlet energyof the first compound.

FIG. 5 exemplarily shows a relationship in energy levels between thefirst compound, the second compound and the third compound in theemitting layer. In FIG. 5, S0 represents a ground state, S1(M1)represents the lowest singlet state of the first compound, T1(M1)represents the lowest triplet state of the first compound, S1(M2)represents the lowest singlet state of the second compound, T1(M2)represents the lowest triplet state of the second compound, S1(M3)represents a lowest singlet state of the third compound, and T1(M3)represents a lowest triplet state of the third compound. A dashed arrowdirected from S1(M1) to S1(M2) in FIG. 5 represents Förster energytransfer from the lowest singlet state of the first compound to thelowest singlet state of the second compound.

As shown in FIG. 5, when a compound having a small ΔST(M1) is used asthe first compound, inverse intersystem crossing from the lowest tripletstate T1(M1) to the lowest singlet state S1(M1) can be caused by a heatenergy. Accordingly, Förster energy transfer from the lowest singletstate S1(M1) of the first compound to the lowest singlet state S1(M2) ofthe second compound is caused. As a result, fluorescence from the lowestsinglet state S1(M2) of the second compound can be observed. It isconsidered that the internal quantum efficiency can be theoreticallyraised up to 100% also by using delayed fluorescence by the TADFmechanism.

Ratio of Three Components

In the emitting layer of the organic EL device of the exemplaryembodiment, it is preferable that the content ratio of the firstcompound is in a range from 10 mass % to 80 mass %, the content ratio ofthe second compound is in a range from 1 mass % to 10 mass %, and thecontent ratio of the third compound is in a range from 10 mass % to 80mass %. The content ratio of the first compound is more preferably in arange from 20 mass % to 80 mass %, further preferably in a range from 40mass % to 60 mass %. An upper limit of the total of the respectivecontent ratios of the first to third compounds in the emitting layer is100 mass %. It should be noted that the emitting layer of the exemplaryembodiment may further contain another material in addition to the firstto third compounds.

Although the third compound is not particularly limited, the thirdcompound is preferably a compound other than an amine compound. Forinstance, a carbazole derivative, dibenzofuran derivative anddibenzothiophene derivative are usable as the third compound. However,the third compound is not limited thereto.

The third compound preferably has at least one of a partial structurerepresented by a formula (31) below and a partial structure representedby a formula (32) below in one molecule.

In the formula (31): Y₃₁ to Y₃₆ each independently represent a nitrogenatom or a carbon atom bonded to another atom in the molecule of thethird compound.

However, at least one of Y₃₁ to Y₃₆ is a carbon atom bonded to anotheratom in the molecule of the third compound.

In the formula (32): Y₄₁ to Y₄₈ each independently represent a nitrogenatom or a carbon atom bonded to another atom in the molecule of thethird compound.

However, at least one of Y₄₁ to Y₄₈ is a carbon atom bonded to anotheratom in the molecule of the third compound.

X₃ represents a nitrogen atom, an oxygen atom or a sulfur atom.

In the formula (32), it is also preferable that at least two of Y₄₁ toY₄₈ are carbon atoms bonded to another atom in the molecule of the thirdcompound and a ring structure is formed including the carbon atoms.

For instance, the partial structure represented by the formula (32) ispreferably a partial structure selected from the group consisting offormulae (321), (322), (323), (324), (325) and (326) below.

In the above formulae (321) to (326), X₃ represents a nitrogen atom, anoxygen atom or a sulfur atom.

Y₄₁ to Y₄₈ each independently represent a nitrogen atom or a carbon atombonded to another atom in the molecule of the third compound.

X₄ represents a nitrogen atom, an oxygen atom, a sulfur atom or a carbonatom.

Y₅₁ to Y₅₄ each independently represent a nitrogen atom or a carbon atombonded to another atom in the molecule of the third compound.

In the exemplary embodiment, the third compound preferably contains thepartial structure represented by the formula (323) among the formulae(321) to (326).

The partial structure represented by the formula (31) is preferably inthe form of at least one group selected from the group consisting ofgroups represented by formulae (33) and (34) below and contained in thethird compound.

For the third compound, bonding positions are preferably both situatedin meta positions as shown in the formulae (33) and (34) to keep anenergy gap T_(77K)(M3) at 77 [K] high.

In the formulae (33) and (34), Y₃₁, Y₃₂, Y₃₄ and Y₃₆ each independentlyrepresent a nitrogen atom or CR₃₁, in which R₃₁ represents a hydrogenatom or a substituent. When R₃₁ is a substituent, the substituent isselected from the group consisting of a substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, asubstituted or unsubstituted heterocyclic group having 5 to 30 ringatoms, a substituted or unsubstituted alkyl group having 1 to 30 carbonatoms, a substituted or unsubstituted fluoroalkyl group having 1 to 30carbon atoms, a substituted or unsubstituted cycloalkyl group having 3to 30 carbon atoms, a substituted or unsubstituted aralkyl group having7 to 30 carbon atoms, a substituted silyl group, a substituted germaniumgroup, a substituted phosphine oxide group, a halogen atom, a cyanogroup, a nitro group, and a carboxy group. However, the substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 ring carbonatoms in R₃₁ is preferably a non-fused ring.

Wavy lines in the formulae (33) and (34) each show a bonding positionwith another atom or another structure in the molecule of the thirdcompound.

In the formula (33), Y₃₁, Y₃₂, Y₃₄ and Y₃₆ are preferably eachindependently CR₃₁. A plurality of R₃₁ may be the same or different.

In the formula (34), Y₃₂, Y₃₄ and Y₃₆ are preferably each independentlyCR₃₁. A plurality of R₃₁ may be the same or different.

The substituted germanium group is preferably represented by —Ge(R₁₀)₃.R₁₀₁ are each independently a substituent. The substituent R₁₀₁ ispreferably a substituted or unsubstituted alkyl group having 1 to 30carbon atoms or a substituted or unsubstituted aromatic hydrocarbongroup having 6 to 30 ring carbon atoms. The plurality of R₁₀₁ may bemutually the same or different

The partial structure represented by the formula (32) is preferably inthe form of at least one group selected from the group consisting ofgroups respectively represented by formulae (35), (36), (37), (38), (39)and (30a) below and contained in the third compound.

In the formulae (35) to (39) and (30a), Y₄₁, Y₄₂, Y₄₃, Y₄₄, Y₄₅, Y₄₆,Y₄₇ and Y₄₈ each independently represent a nitrogen atom or CR₃₂.

R₃₂ represents a hydrogen atom or a substituent. When R₃₂ is asubstituent, the substituent is selected from the group consisting of asubstituted or unsubstituted aromatic hydrocarbon group having 6 to 30ring carbon atoms, a substituted or unsubstituted heterocyclic grouphaving 5 to 30 ring atoms, a substituted or unsubstituted alkyl grouphaving 1 to 30 carbon atoms, a substituted or unsubstituted fluoroalkylgroup having 1 to 30 carbon atoms, a substituted or unsubstitutedcycloalkyl group having 3 to 30 carbon atoms, a substituted orunsubstituted aralkyl group having 7 to 30 carbon atoms, a substitutedsilyl group, a substituted germanium group, a substituted phosphineoxide group, a halogen atom, a cyano group, a nitro group, and a carboxygroup. However, the substituted or unsubstituted aromatic hydrocarbongroup having 6 to 30 ring carbon atoms in R₃₂ is preferably a non-fusedring.

X₃ in the formulae (35) and (36) represents a nitrogen atom.

X₃ in the formulae (37) to (39) and (30a) represents NR₃₃, an oxygenatom or a sulfur atom.

R₃₃ is a substituent selected from the group consisting of a substitutedor unsubstituted aromatic hydrocarbon group having 6 to 30 ring carbonatoms, a substituted or unsubstituted heterocyclic group having 5 to 30ring atoms, a substituted or unsubstituted alkyl group having 1 to 30carbon atoms, a substituted or unsubstituted fluoroalkyl group having 1to 30 carbon atoms, a substituted or unsubstituted cycloalkyl grouphaving 3 to 30 carbon atoms, a substituted or unsubstituted aralkylgroup having 7 to 30 carbon atoms, a substituted silyl group, asubstituted germanium group, a substituted phosphine oxide group, afluorine atom, a cyano group, a nitro group, and a carboxy group.However, the substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms in R₃₃ is preferably a non-fused ring.

Wavy lines in the formulae (35) to (39) and (30a) each show a bondingposition with another atom or another structure in the molecule of thethird compound.

In the formula (35), Y₄₁ to Y₄₈ are preferably each independently CR₃₂.In the formulae (36) and (37), Y₄₁ to Y₄₅, Y₄₇ and Y₄₈ are preferablyeach independently CR₃₂. In the formula (38), Y₄₁, Y₄₂, Y₄₄, Y₄₅, Y₄₇and Y₄₈ are preferably each independently CR₃₂. In the formula (39), Y₄₂to Y₄₈ are preferably each independently CR₃₂. In the formula (30a), Y₄₂to Y₄₇ are preferably each independently CR₃₂. A plurality of R₃₂ may bethe same or different.

In the third compound, X₃ is preferably an oxygen atom or a sulfur atom,more preferably an oxygen atom.

In the third compound, R₃₁ and R₃₂ each independently represent ahydrogen atom or a substituent. The substituent in R₃₁ and R₃₂ ispreferably selected from the group consisting of a fluorine atom, acyano group, a substituted or unsubstituted alkyl group having 1 to 30carbon atoms, a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms, and a substituted or unsubstitutedheterocyclic group having 5 to 30 ring atoms. More preferably R₃₁ andR₃₂ are a hydrogen atom, a cyano group, a substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms, or asubstituted or unsubstituted heterocyclic group having 5 to 30 ringatoms. The substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms in R₃₁ and R₃₂ is preferably anon-fused ring.

The third compound is also preferably an aromatic hydrocarbon compoundor an aromatic heterocyclic compound. It is also preferable that thethird compound has no fused aromatic hydrocarbon ring in a molecule.

Method of Preparing Third Compound

The third compound may be prepared by a method described inInternational Publications WO2012/153780, WO2013/038650 and the like.

Examples of the substituent in the third compound are shown below, butthe invention is not limited thereto.

Specific examples of the aromatic hydrocarbon group (occasionallyreferred to as an aryl group) include a phenyl group, tolyl group, xylylgroup, naphthyl group, phenanthryl group, pyrenyl group, chrysenylgroup, benzo[c]phenanthryl group, benzo[g]chrysenyl group, benzoanthrylgroup, triphenylenyl group, fluorenyl group, 9,9-dimethylfluorenylgroup, benzofluorenyl group, dibenzofluorenyl group, biphenyl group,terphenyl group, quarterphenyl group and fluoranthenyl group, amongwhich a phenyl group, biphenyl group, terphenyl group, quarterphenylgroup, naphthyl group, triphenylenyl group and fluorenyl group may bepreferable.

Specific examples of the substituted aromatic hydrocarbon group includea tolyl group, xylyl group and 9,9-dimethylfluorenyl group.

As is understood from the specific examples, the aryl group includesboth fused aryl group and non-fused aryl group.

Preferable examples of the aromatic hydrocarbon group include a phenylgroup, biphenyl group, terphenyl group, quarterphenyl group, naphthylgroup, triphenylenyl group and fluorenyl group.

Specific examples of the aromatic heterocyclic group (occasionallyreferred to as a heteroaryl group, heteroaromatic ring group orheterocyclic group) include a pyrrolyl group, pyrazolyl group, pyrazinylgroup, pyrimidinyl group, pyridazynyl group, pyridyl group, triazinylgroup, indolyl group, isoindolyl group, imidazolyl group, benzimidazolylgroup, indazolyl group, imidazo[1,2-a]pyridinyl group, furyl group,benzofuranyl group, isobenzofuranyl group, dibenzofuranyl group,azadibenzofuranyl group, thiophenyl group, benzothiophenyl group,dibenzothiophenyl group, azadibenzothiophenyl group, quinolyl group,isoquinolyl group, quinoxalinyl group, quinazolinyl group,naphthyridinyl group, carbazolyl group, azacarbazolyl group,phenanthridinyl group, acridinyl group, phenanthrolinyl group,phenazinyl group, phenothiazinyl group, phenoxazinyl group, oxazolylgroup, oxadiazolyl group, furazanyl group, benzoxazolyl group, thienylgroup, thiazolyl group, thiadiazolyl group, benzothiazolyl group,triazolyl group and tetrazolyl group, among which a dibenzofuranylgroup, dibenzothiophenyl group, carbazolyl group, pyridyl group,pyrimidinyl group, triazinyl group, azadibenzofuranyl group andazadibenzothiophenyl group may be preferable.

The aromatic heterocyclic group is preferably any one of adibenzofuranyl group, dibenzothiophenyl group, carbazolyl group, pyridylgroup, pyrimidinyl group, triazinyl group, azadibenzofuranyl group andazadibenzothiophenyl group, and further preferably any one of adibenzofuranyl group, dibenzothiophenyl group, azadibenzofuranyl groupand azadibenzothiophenyl group.

In the third compound, the substituted silyl group is also preferably asubstituted or unsubstituted trialkylsilyl group, a substituted orunsubstituted arylalkylsilyl group, or a substituted or unsubstitutedtriarylsilyl group.

Specific examples of the substituted or unsubstituted trialkylsilylgroup include a trimethylsilyl group and a triethysilyl group.

Specific examples of the substituted or unsubstituted arylalkylsilylgroup include a diphenylmethylsilyl group, ditolylmethylsilyl group, andphenyldimethylsilyl group.

Specific examples of the substituted or unsubstituted triarylsilyl groupinclude a triphenylsilyl group and a tritolylsilyl group.

In the third compound, the substituted phosphine oxide group is alsopreferably a substituted or unsubstituted diarylphosphine oxide group.

Specific examples of the substituted or unsubstituted diarylphosphineoxide group include a diphenylphosphine oxide group and ditolylphosphineoxide group.

The organic EL device in the exemplary embodiment is capable ofprolonging a lifetime, improving a luminous efficiency, and inhibiting aroll-off when driven at a high current density.

The emitting layer of the organic EL device according to the secondexemplary embodiment includes the delayed fluorescent first compound,the fluorescent second compound, and the third compound having a largersinglet energy than the first compound, whereby the luminous efficiencyof the organic EL device is further improved. It is deduced that theluminous efficiency is improved because a carrier balance in theemitting layer is improved by containing the third compound.

Third Exemplary Embodiment

Arrangement(s) of an organic EL device according to a third exemplaryembodiment will be described below. In the description of the thirdexemplary embodiment, the same components as those in the firstexemplary embodiment are denoted by the same reference signs and namesto simplify or omit an explanation of the components. In the thirdexemplary embodiment, the same materials and compounds as described inthe first exemplary embodiment are usable for a material and a compoundwhich are not particularly described.

In the third exemplary embodiment, the emitting layer of the organic ELdevice includes the first compound and the second compound, in which thefirst compound is a delayed fluorescent compound and the second compoundis a fluorescent compound. An ionization potential Ip1 of the firstcompound and an ionization potential Ip2 of the second compound satisfya relationship represented by a numerical formula (Numerical Formula 3).Ip1 and Ip2 preferably satisfy a numerical formula (Numerical Formula3A).0≤Ip2−Ip1≤0.3 eV  (Numerical Formula 3)0<Ip2−Ip1≤0.3 eV  (Numerical Formula 3A)

The first compound in the first exemplary embodiment is defined in termsof a predetermined emission quantum efficiency, whereas the firstcompound in the third exemplary embodiment is not defined in terms ofthe emission quantum efficiency as long as being a delayed fluorescentcompound. Other components in the third exemplary embodiment are thesame as those in the first exemplary embodiment.

In the organic EL device of the third exemplary embodiment, the emittinglayer may further include the third compound described in the secondexemplary embodiment.

When the numerical formula (Numerical Formula 3) is satisfied, the trapemission can be inhibited. When the trap emission is inhibited, arecombination of holes and electrons is promoted by the first compoundthat is the delayed fluorescent compound. Energy transfer quickly occursfrom the first compound in the excited state to the second compound,whereby the first compound is returned to the ground state and thesecond compound is brought into the excited state. When the secondcompound in the excited state is returned to the ground state, light isirradiated. As described above, also in the exemplary embodiment, sincethe recombination of holes and electrons in the first compound ispromoted, it is deduced that excitons for contributing to emission fromthe second compound are increased, resulting in an improvement in theluminous efficiency.

Further, since the trap emission by the second compound is inhibited,carriers (holes and electrons) are inhibited from colliding againstexcitons (singlet excitons and triplet excitons). As a result, it isdeduced that, although the number of the carriers in the emitting layeris increased in the high current density region as compared with in thelow current density region, a roll-off in the high current densityregion is also inhibited because the organic EL device of the exemplaryembodiment can inhibit the carriers and the excitons from colliding tobe deactivated.

Modification of Embodiments

It should be noted that the invention is not limited to the exemplaryembodiment. The invention may include any modification and improvementcompatible with the invention.

For instance, the emitting layer is not limited to a single layer, butmay be provided by laminating a plurality of emitting layers. When theorganic EL device has the plurality of emitting layers, it is onlyrequired that at least one of the emitting layers contains the first andsecond compounds. For instance, the rest of the emitting layers may be afluorescent emitting layer or a phosphorescent emitting layer with useof emission caused by electron transfer from the triplet state directlyto the ground state.

When the organic EL device includes the plurality of emitting layers,the plurality of emitting layers may be adjacent to each other, orprovide a so-called tandem-type organic EL device in which a pluralityof emitting units are layered through an intermediate layer.

For instance, a blocking layer may be provided in contact with ananode-side or a cathode-side of the emitting layer. The blocking layeris preferably provided in contact with the emitting layer to block atleast ones of holes, electrons and excitons.

For instance, when the blocking layer is provided in contact with thecathode-side of the emitting layer, the blocking layer permits transportof electrons, but prevents holes from reaching a layer provided near thecathode (e.g., the electron transporting layer) beyond the blockinglayer. When the organic EL device includes the electron transportinglayer, the blocking layer is preferably interposed between the emittinglayer and the electron transporting layer.

When the blocking layer is provided in contact with the anode-side ofthe emitting layer, the blocking layer permits transport of holes, butprevents electrons from reaching a layer provided near the anode (e.g.,the hole transporting layer) beyond the blocking layer. When the organicEL device includes the hole transporting layer, the blocking layer ispreferably interposed between the emitting layer and the holetransporting layer.

Further, the blocking layer may be provided in contact with the emittinglayer to prevent an excitation energy from leaking from the emittinglayer into a layer in the vicinity thereof. Excitons generated in theemitting layer are prevented from moving into a layer provided near theelectrode (e.g., the electron transporting layer and the holetransporting layer) beyond the blocking layer.

The emitting layer and the blocking layer are preferably bonded to eachother.

Further, the materials and treatments for practicing the invention maybe altered to other arrangements and treatments as long as such otherarrangements and treatments are compatible with the invention.

EXAMPLES

Examples of the invention will be described below. However, theinvention is not limited to Examples.

Compounds used for preparing the organic EL device will be shown below.

Evaluation of Compounds

Next, properties of the compounds used in Example were measured. Ameasurement method and a calculation method are shown below.

Measurement Method of Ionization Potential

A photoelectron spectroscopy device (AC-3, manufactured by Riken KeikiCo., Ltd.) was used for the measurement of an ionization potential underatmosphere. Specifically, a compound to be measured was irradiated withlight and the amount of electrons generated by charge separation wasmeasured.

Measurement Method of Emission Quantum Efficiency

An emission quantum efficiency D was measured as follows.

A sample (i.e., measurement target) was dissolved in a solvent oftoluene to prepare a sample solution. The prepared sample solution wasput into a 1-cm cell. An absorption spectrum of the cell was measuredusing an absorptiometer. An excitation wavelength in the luminescencespectrum measurement was determined based on the measured absorptionspectrum. It should be noted that the excitation wavelength is desirablya wavelength providing an absorption peak, but not limited thereto. Aconcentration of the sample solution is desirably weak to inhibit theemission from being re-absorbed. In the present measurement, theconcentration of the sample solution was prepared such that anabsorbance in the excitation wavelength was 0.05 or less.

The sample solution as prepared above was put into a glass sample pipeprovided with a vacuum stopcock. This sample pipe was connected to avacuum line provided with a vacuum pump and a vacuum gauge and wassubjected to freeze-deaeration. The freeze-deaeration in the presentmeasurement refers to an operation in which a solution-accumulatingportion of the sample pipe is soaked in liquid nitrogen to freeze thesample solution and an inside of the sample pipe is vacuumized.Moreover, in the present measurement, a rotary pump was used as thevacuum pump and a pirani vacuum gauge was used as the vacuum gauge. Itshould be noted that the vacuum pump and the vacuum gauge are notlimited to the vacuum pump and the vacuum gauge used in the presentmeasurement.

After the freeze-deaeration, the sample solution was dissolved at theroom temperature and was again subjected to the freeze-deaeration. Thisoperation was repeated until no change in the vacuum degree wasobserved. The solution obtained as a result of the repeated operationwas defined as a deaeration sample solution.

The sample pipe containing the deaeration sample solution and a 1-cmlidded cell were put into a glove box. Under inactive gas (e.g.,nitrogen) atmosphere in the glove box, the deaeration sample solutionwas transferred from the sample pipe to the lidded cell and the liddedcell was hermetically sealed. After hermetically sealed, the lidded cellwas taken out of the glove box. A luminescence spectrum of thedeaeration sample solution was measured using a fluorometer. A lineconnecting a rise of the obtained luminescence spectrum on ashort-wavelength side and a rise thereof on a long-wavelength side wasdefined as a reference line and an area intensity F₁ of the emission wascalculated.

The above processes were also performed on a standard sample having aknown emission quantum efficiency and an area intensity F₂ of theemission of the deaeration standard sample solution was calculated.

An emission quantum efficiency Φ of the target sample was obtainedaccording to a formula A below.Φ=Φ₂×{(F ₁ A ₂ n ₁ ²)/(F ₂ A ₁ n ₂ ²)}  (Formula A)

Herein, in the formula A, Φ₂ represents an emission quantum efficiencyof the standard sample, A₁ represents an absorbance of the samplesolution in the excitation wavelength, A₂ represents an absorbance ofthe standard sample solution in the excitation wavelength, n₁ representsa refractive index of a solvent used for preparing the sample solution,and n₂ represents a refractive index of a solvent used for preparing thestandard sample solution.

In Example, an ethanol solution of 9,10-diphenyl anthracene was used asthe standard sample solution and Φ₂=0.95 was determined (Morris et al.,J. Phys. Chem., 80(1976)969.).

Moreover, n₁ and n₂ were determined as n₁=1.498 (toluene) and n₂=1.362(ethanol) (“Kagaku Binran (Handbook of Chemistry) Basic” the revised5^(th) edition, Chapter 14, II-640 page, issued on Feb. 1, 2004).

An absorptiometer (device name: UV-3100PC) manufactured by ShimadzuCorporation was used as an absorption spectrum measurement device. Afluorometer (device name: F-4500) manufactured by Hitachi, Ltd. was usedas a luminescence spectrum measurement device.

The standard sample solution is not particularly limited to the solutionused in the present measurement as long as having the known emissionquantum efficiency. Moreover, the solvent is not limited to the solventused in the present measurement. The absorption spectrum measuringdevice and the luminescence spectrum measurement device are not limitedto the above devices used in the present measurement.

Measurement results of the ionization potential and the emission quantumefficiency are shown in Table 2. The emission quantum efficiency isexpressed in a unit of percentage. It should be noted that Table 2 showsan emission quantum efficiency of a compound H-2 exceeding 99%.

TABLE 2 Ionization Potential Emission Quantum Compound (eV) Efficiency(%) H-1 5.60 63   H-2 5.61 99< D-1 5.64 — D-2 5.48 — D-3 6.45 —Delayed Fluorescence Emission

Occurrence of delayed fluorescence emission was determined by measuringtransient photoluminescence (PL) using a device shown in FIG. 2. Asample was prepared by co-depositing the compounds H-1 and TH-2 on aquartz substrate at a ratio of the compound H-1 being 12 mass % to forma 100-nm-thick thin film. Emission from the compound H-1 include: Promptemission observed immediately when the excited state is achieved byexciting the compound H-1 with a pulse beam (i.e., a beam emitted from apulse laser) having an absorbable wavelength; and Delay emissionobserved not immediately when but after the excited state is achieved.Delayed fluorescence emission in the exemplary embodiment means that theamount of Delay emission is 5% or more relative to the amount of Promptemission.

It has been confirmed that the amount of Delay emission of the compoundH-1 is 5% or more relative to the amount of Prompt emission.

The amount of Prompt emission and the amount of Delay emission can beobtained in the same method as a method described in “Nature 492,234-238, 2012.” The amount of Prompt emission and the amount of Delayemission may be calculated using a device different from ones shown inFIG. 2 and described in Reference Literatures.

Singlet Energy S

The singlet energy S was measured as follows. 10 μmol/L of a toluenesolution containing the target compound for the measurement was preparedand put in a quartz cell to prepare a sample. An absorption spectrum(ordinate axis: luminous intensity, abscissa axis: wavelength) of thesample was measured at a normal temperature (300K). A tangent was drawnto the fall of the absorption spectrum on the long-wavelength side, anda wavelength value λedge [nm] at an intersection of the tangent and theabscissa axis was substituted in the following conversion equation tocalculate a singlet energy.S[eV]=1239.85/λedge  Conversion Equation 2:

In Example, the absorption spectrum was measured using aspectrophotometer manufactured by Hitachi, Ltd. (device name: U3310). Itshould be noted that the absorption spectrum measuring device may bedifferent from the above device.

The calculated singlet energy S is shown below.

H-1: 2.74 eV

H-2: 2.89 eV

DA: 3.55 eV

Preparation and Evaluation of Organic EL Device

The organic EL devices were prepared in the following manner andevaluated.

Example 1

A glass substrate (size: 25 mm×75 mm×1.1 mm thick, manufactured byGeomatec Co., Ltd.) having an ITO transparent electrode (anode) wasultrasonic-cleaned in isopropyl alcohol for five minutes, and thenUV/ozone-cleaned for 30 minutes. A film of ITO was 130 nm thick.

After the glass substrate having the transparent electrode line wascleaned, the glass substrate was mounted on a substrate holder of avacuum evaporation apparatus. Initially, a compound HI was deposited ona surface of the glass substrate where the transparent electrode linewas provided in a manner to cover the transparent electrode, therebyforming a 5-nm-thick hole injecting layer.

Subsequently, a compound HT-1 was deposited on the hole injecting layerto form a 110-nm-thick first hole transporting layer on the HI film.

Next, a compound HT-2 was deposited on the first hole transporting layerto form a 15-nm-thick second hole transporting layer.

Next, a compound DA, the compound H-1 and a compound D-1 wereco-deposited on the second hole transporting layer to form a 25-nm-thickemitting layer. In the emitting layer, a concentration of the compoundH-1 was set to be 50 mass % and a concentration of the compound D-1 wasset to be 1 mass %.

Next, a compound HB-1 was deposited on the emitting layer to form a5-nm-thick hole blocking layer.

Next, a compound ET-1 was deposited on the hole blocking layer to form a35-nm-thick electron transporting layer.

Lithium fluoride (LiF) was then deposited on the electron transportinglayer to form a 1-nm-thick electron injecting electrode (cathode).

A metal aluminum (Al) was then deposited on the electron injectingelectrode to form an 80-nm-thick metal Al cathode.

A device arrangement of the organic EL device in Example 1 isschematically shown as follows.

ITO(130)/HI(5)/HT-1(110)/HT-2(15)/DA:H-1:D-1(25, 50%,1%)/HB-1(5)/ET-1(35)/LiF(1)/Al(80)

Numerals in parentheses represent a film thickness (unit: nm). Thenumerals in the form of percentage in parentheses indicate ratios (mass%) of the first and second compounds in the emitting layer.

Comparative 1

An organic EL device of Comparative 1 was manufactured in the samemanner as the organic EL device of Example 1 except that a compound D-2was used in place of the compound D-1 in the emitting layer of Example1.

A device arrangement of the organic EL device of Comparative 1 isroughly shown as follows.

ITO(130)/HI(5)/HT-1(110)/HT-2(15)/DA:H-1:D-2(25, 50%,1%)/HB-1(5)/ET-1(35)/LiF(1)/Al(80)

Comparative 2

An organic EL device of Comparative 2 was manufactured in the samemanner as the organic EL device of Example 1 except that a compound D-3was used in place of the compound D-1 in the emitting layer of Example1.

A device arrangement of the organic EL device of Comparative 2 isroughly shown as follows.

ITO(130)/HI(5)/HT-1(110)/HT-2(15)/DA:H-1:D-3(25, 50%,1%)/HB-1(5)/ET-1(35)/LiF(1)/Al(80)

Comparative 3

An organic EL device of Comparative 3 was manufactured in the samemanner as the organic EL device of Example 1 except that the compoundH-2 was used in place of the compound H-1 in the emitting layer ofExample 1.

A device arrangement of the organic EL device of Comparative 3 isroughly shown as follows.

ITO(130)/HI(5)/HT-1(110)/HT-2(15)/DA:H-2:D-1(25, 50%,1%)/HB-1(5)/ET-1(35)/LiF(1)/Al(80)

Comparative 4

An organic EL device of Comparative 4 was manufactured in the samemanner as the organic EL device of Comparative 3 except that thecompound D-2 was used in place of the compound D-1 in the emitting layerof Comparative 3.

A device arrangement of the organic EL device of Comparative 4 isroughly shown as follows.

ITO(130)/HI(5)/HT-1(110)/HT-2(15)/DA:H-2:D-2(25, 50%,1%)/HB-1(5)/ET-1(35)/LiF(1)/Al(80)

Comparative 5

An organic EL device of Comparative 5 was manufactured in the samemanner as the organic EL device of Comparative 3 except that thecompound D-3 was used in place of the compound D-1 in the emitting layerof Comparative 3.

A device arrangement of the organic EL device of Comparative 5 isroughly shown as follows.

ITO(130)/HI(5)/HT-1(110)/HT-2(15)/DA:H-2:D-3(25, 50%,1%)/HB-1(5)/ET-1(35)/LiF(1)/Al(80)

Evaluation of Organic EL Devices

The organic EL devices manufactured in Example 1 and Comparatives 1 to 5were evaluated as follows. Evaluation results are shown in Tables 3 and4.

CIE1931 Chromaticity

Voltage was applied on each of the manufactured organic EL devices suchthat the current density was 0.1 mA/cm², 1 mA/cm² or 10 mA/cm², whereCIE1931 chromaticity coordinates (x, y) were measured using aspectroradiometer (manufactured by Konica Minolta, Inc., product name:CS-1000).

External Quantum Efficiency EQE

Voltage was applied on each of the organic EL devices such that thecurrent density was 0.1 mA/cm², 1 mA/cm² or 10 mA/cm², where spectralradiance spectrum was measured using the above spectroradiometer. Theexternal quantum efficiency EQE (unit: %) was calculated based on theobtained spectral-radiance spectrum, assuming that Lambertian radiationwas performed.

Main Peak Wavelength λ_(p)

A main peak wavelength λ_(p) was calculated based on the obtainedspectral-radiance spectra.

Lifetime LT80

An initial current density was set at 50 mA/cm² and a continuous currenttest was performed. A time elapsed until a luminance intensity wasreduced to 80% of an initial luminance intensity at the start of thetest was defined as a lifetime (LT80).

Roll-Off

Each of the organic EL devices of Example 1 and Comparatives 1, 3 and 4was driven under the driving conditions of the current densities at 0.1mA/cm², 1 mA/cm² and 10 mA/cm². A ratio of the external quantumefficiency under each of the driving conditions relative to the highestexternal quantum efficiency among the obtained external quantumefficiencies was calculated.

TABLE 3 Current Density Chromaticity EQE λ_(p) Roll- (mA/cm²) x y (%)(nm) Off Example 1 0.10 0.316 0.627 11.49 530 0.96 1.00 0.314 0.62711.94 530 1.00 10 0.311 0.626 11.25 530 0.94 Comparative 1 0.10 0.3480.627 5.26 536 1.00 1.00 0.346 0.627 4.89 536 0.93 10 0.344 0.626 4.29536 0.82 Comparative 2 0.10 0.248 0.678 2.57 519 — 1.00 0.250 0.668 2.79519 10 0.251 0.653 2.82 518 Comparative 3 0.10 0.302 0.624 12.05 5290.97 1.00 0.301 0.623 12.37 529 1.00 10 0.299 0.622 11.53 529 0.93Comparative 4 0.10 0.342 0.624 4.71 536 1.00 1.00 0.340 0.624 4.41 5360.94 10 0.338 0.622 3.88 536 0.82 Comparative 5 0.10 0.230 0.682 2.55519 — 1.00 0.227 0.669 2.63 519 10 0.225 0.650 2.63 518

TABLE 4 LT80 (hrs) Example 1 40 Comparative 1 25 Comparative 2 5Comparative 3 27 Comparative 4 22 Comparative 5 4

As shown in Tables 3 and 4, as compared with the organic EL devices ofComparatives 1 to 5, the organic EL device of Example 1 exhibited ahigher external quantum efficiency and a longer lifetime and inhibitedroll-off when driven at a high current density.

EXPLANATION OF CODES

-   -   1: organic EL device, 3: anode, 4: cathode, 5: emitting layer.

The invention claimed is:
 1. An organic electroluminescence devicecomprising: an anode; an emitting layer; and a cathode, wherein theemitting layer comprises a first compound, a second compound, and athird compound, the first compound is a delayed fluorescent compound,the second compound is a fluorescent compound, an emission quantumefficiency of the first compound is in a range from 30% to 70%, anionization potential Ip1 of the first compound and an ionizationpotential Ip2 of the second compound satisfy a relationship of0≤Ip2−Ip1≤0.8 eV, a singlet energy of the third compound is larger thana singlet energy of the first compound, the first compound is a compoundrepresented by a formula (1) below, the second compound is abisarylamino pyrene derivative, a pyrromethene boron complex compound,or a compound having a pyrromethene skeleton, and the third compoundcomprises at least one of a partial structure represented by a formula(31) below and a partial structure represented by a formula (32) belowin one molecule,

where: A is an acceptor moiety and is a group comprising a partialstructure selected from partial structures represented by formulae (a-1)and (a-2); B is a donor moiety and comprises a partial structureselected from partial structures represented by formulae (b-1) to (b-4);a, b and d are each independently an integer from 1 to 5; c is aninteger from 0 to 5; when c is 0, A is bonded to B by a single bond or aspiro bond; when c is an integer from 1 to 5, L is a linking groupselected from the group consisting of a substituted or unsubstitutedaromatic hydrocarbon group having 6 to 30 ring carbon atoms and asubstituted or unsubstituted heterocyclic group having 5 to 30 ringatoms; when a plurality of A are present, the plurality of A aremutually the same or different, and are bonded to to form a saturated orunsaturated ring or not bonded; when a plurality of B are present, theplurality of B are mutually the same or different, and are bonded to toform a saturated or unsaturated ring or not bonded; and when a pluralityof L are present, the plurality of L are mutually the same or different,and are bonded to to form a saturated or unsaturated ring or not bonded,

 in the formulae (b-1) to (b-4): R is each independently a hydrogen atomor a substituent; when R is a substituent, the substituent is selectedfrom the group consisting of a substituted or unsubstituted aromatichydrocarbon group having 6 to 30 ring carbon atoms, a substituted orunsubstituted heterocyclic group having 5 to 30 ring atoms, and asubstituted or unsubstituted alkyl group having 1 to 30 carbon atoms;and when a plurality of R are present, the plurality of R are mutuallythe same or different and optionally bonded to each other to form asaturated or unsaturated ring,

 in the formula (31): Y₃₁ to Y₃₆ each independently represent a nitrogenatom or a carbon atom bonded to another atom in the molecule of thethird compound; and at least one of Y₃₁ to Y₃₆ is a carbon atom bondedto another atom in the molecule of the third compound, and in theformula (32): Y₄₁ to Y₄₈ each independently represent a nitrogen atom ora carbon atom bonded to another atom in the molecule of the thirdcompound; at least one of Y₄₁ to Y₄₈ is a carbon atom bonded to anotheratom in the molecule of the third compound; and X₃ represents a nitrogenatom, an oxygen atom or a sulfur atom.
 2. The organicelectroluminescence device according to claim 1, wherein the ionizationpotential Ip1 of the first compound and the ionization potential Ip2 ofthe second compound satisfy a relationship of0≤Ip2−Ip1≤0.5 eV.
 3. The organic electroluminescence device according toclaim 1, wherein the emission quantum efficiency of the first compoundis 65% or less.
 4. The organic electroluminescence device according toclaim 1, wherein the emission quantum efficiency of the first compoundis 60% or less.
 5. The organic electroluminescence device according toclaim 1, wherein a singlet energy of the first compound is larger than asinglet energy of the second compound.
 6. The organicelectroluminescence device according to claim 1, wherein the secondcompound has an emission peak wavelength of 550 nm or less.
 7. Theorganic electroluminescence device according to claim 1, furthercomprising: a hole transporting layer between the anode and the emittinglayer.
 8. The organic electroluminescence device according to claim 1,further comprising: an electron transporting layer between the emittinglayer and the cathode.
 9. The organic electroluminescence deviceaccording to claim 1, wherein the ionization potential Ip1 of the firstcompound and the ionization potential Ip2 of the second compound satisfya relationship of0≤Ip2−Ip1≤0.8 eV.
 10. The organic electroluminescence device accordingto claim 1, wherein the ionization potential Ip1 of the first compoundand the ionization potential Ip2 of the second compound satisfy arelationship of0≤Ip2−Ip1≤0.5 eV.
 11. The organic electroluminescence device accordingto claim 1, wherein the first compound is not a metal complex.
 12. Theorganic electroluminescence device according to claim 1, wherein theemitting layer does not comprise a phosphorescent metal complex.
 13. Theorganic electroluminescence device according to claim 1, wherein acontent ratio of the first compound in the emitting layer is in a rangefrom 40 mass % to 60 mass %.
 14. The organic electroluminescence deviceaccording to claim 1, wherein the ionization potential Ip1 of the firstcompound and the ionization potential Ip2 of the second compound satisfya relationship of0≤Ip2−Ip1≤0.8 eV, and the emitting layer does not comprise aphosphorescent metal complex.
 15. The organic electroluminescence deviceaccording to claim 1, wherein the singlet energy of the first compoundis larger than a singlet energy of the second compound, the secondcompound has an emission peak wavelength of 550 nm or less, theionization potential Ip1 of the first compound and the ionizationpotential Ip2 of the second compound satisfy a relationship of0≤Ip2−Ip1≤0.5 eV, and the emitting layer does not comprise aphosphorescent metal complex.
 16. The organic electroluminescence deviceaccording to claim 1, wherein B in the formula (1) is a group having thepartial structure represented by the formulae (b-2).
 17. The organicelectroluminescence device according to claim 1, wherein A in theformula (1) is a group having the partial structure represented by theformulae (a-2).
 18. The organic electroluminescence device according toclaim 1, wherein in the formula (1): a is an integer from 1 to 2; b isan integer from 1 to 4; c is 0 or 1; and d is 1 or
 2. 19. The organicelectroluminescence device according to claim 1, wherein a bondingpattern of the compound represented by the formula (1) is represented bya formula (1B) below,B-L-A  (1B) where: B, L and A respectively represent the same as B, Land A in the formula (1).
 20. The organic electroluminescence deviceaccording to claim 1, wherein L in the formula (1) is a linking groupselected from a substituted or unsubstituted aromatic hydrocarbon grouphaving 6 to 30 ring carbon atoms.
 21. The organic electroluminescencedevice according to claim 1, wherein the second compound is apyrromethene boron complex compound or a compound having a pyrrometheneskeleton.
 22. The organic electroluminescence device according to claim1, wherein the second compound is a compound represented by a formula(10) below,

where: A_(D) is a substituted or unsubstituted aromatic hydrocarbongroup having 12 to 50 ring carbon atoms; B_(D) is a group represented bya formula (11) below; pa is an integer from 1 to 4; pb is an integerfrom 0 to 4; when a plurality of A_(D) are present, the plurality ofA_(D) are mutually the same or different; when a plurality of B_(D) arepresent, the plurality of B_(D) are mutually the same or different; andwhen a plurality of Ar₃ are present, the plurality of Ar₃ are mutuallythe same or different,

where: Ar₁, Ar₂ and Ar₃ each independently represent a substituentselected from the group consisting of a substituted or unsubstitutedaromatic hydrocarbon group having 6 to 50 ring carbon atoms, asubstituted or unsubstituted alkyl group having 1 to 50 carbon atoms, asubstituted or unsubstituted alkenyl group having 2 to 20 carbon atoms,a substituted or unsubstituted alkynyl group having 2 to 20 carbonatoms, and a substituted or unsubstituted heterocyclic group having 5 to50 ring atoms; pc is an integer from 0 to 4; when a plurality of Ar₁ arepresent, the plurality of Ar₁ are mutually the same or different; when aplurality of Ar₂ are present, the plurality of Ar₂ are mutually the sameor different; and when a plurality of Ar₃ are present, the plurality ofAr₃ are mutually the same or different.
 23. The organicelectroluminescence device according to claim 22, wherein in the formula(10), A_(D) is a group selected from the group consisting of groupsderived from a substituted or unsubstituted naphthalene, a substitutedor unsubstituted anthracene, a substituted or unsubstitutedbenzanthracene, a substituted or unsubstituted phenanthrene, asubstituted or unsubstituted chrysene, a substituted or unsubstitutedpyrene, a substituted or unsubstituted fluoranthene, a substituted orunsubstituted benzofluoranthene, a substituted or unsubstitutedperylene, a substituted or unsubstituted picene, a substituted orunsubstituted triphenylene, a substituted or unsubstituted fluorene, asubstituted or unsubstituted benzofluorene, a substituted orunsubstituted stilbene and a substituted or unsubstituted naphthacene.24. The organic electroluminescence device according to claim 1, whereinthe partial structure represented by the formula (31) in a form of atleast one group selected from the group consisting of groups representedby formulae (33) and (34) below is contained in the third compound,

where: Y₃₁, Y₃₂, Y₃₄ and Y₃₆ each independently represent a nitrogenatom or CR₃₁; R₃₁ represents a hydrogen atom or a substituent; when R₃₁is a substituent, the substituent is selected from the group consistingof a substituted or unsubstituted aromatic hydrocarbon group having 6 to30 ring carbon atoms, a substituted or unsubstituted heterocyclic grouphaving 5 to 30 ring atoms, a substituted or unsubstituted alkyl grouphaving 1 to 30 carbon atoms, a substituted or unsubstituted fluoroalkylgroup having 1 to 30 carbon atoms, a substituted or unsubstitutedcycloalkyl group having 3 to 30 carbon atoms, a substituted orunsubstituted aralkyl group having 7 to 30 carbon atoms, a substitutedsilyl group, a substituted germanium group, a substituted phosphineoxide group, a halogen atom, a cyano group, a nitro group, and a carboxygroup.
 25. The organic electroluminescence device according to claim 1,wherein the partial structure represented by the formula (32) in a formof at least one group selected from the group consisting of groupsrespectively represented by formulae (35), (36), (37), (38), (39) and(30a) below is contained in the third compound,

where: Y₄₁, Y₄₂, Y₄₃, Y₄₄, Y₄₅, Y₄₆, Y₄₇ and Y₄₈ each independentlyrepresent a nitrogen atom or CR₃₂; R₃₂ represents a hydrogen atom or asubstituent; when R₃₂ is a substituent, the substituent is selected fromthe group consisting of a substituted or unsubstituted aromatichydrocarbon group having 6 to 30 ring carbon atoms, a substituted orunsubstituted heterocyclic group having 5 to 30 ring atoms, asubstituted or unsubstituted alkyl group having 1 to 30 carbon atoms, asubstituted or unsubstituted fluoroalkyl group having 1 to 30 carbonatoms, a substituted or unsubstituted cycloalkyl group having 3 to 30carbon atoms, a substituted or unsubstituted aralkyl group having 7 to30 carbon atoms, a substituted silyl group, a substituted germaniumgroup, a substituted phosphine oxide group, a halogen atom, a cyanogroup, a nitro group, and a carboxy group; X₃ in the formulae (35) and(36) represents a nitrogen atom; X₃ in the formulae (37) to (39) and(30a) represents NR₃₃, an oxygen atom or a sulfur atom; and R₃₃ is asubstituent selected from the group consisting of a substituted orunsubstituted aromatic hydrocarbon group having 6 to 30 ring carbonatoms, a substituted or unsubstituted heterocyclic group having 5 to 30ring atoms, a substituted or unsubstituted alkyl group having 1 to 30carbon atoms, a substituted or unsubstituted fluoroalkyl group having 1to 30 carbon atoms, a substituted or unsubstituted cycloalkyl grouphaving 3 to 30 carbon atoms, a substituted or unsubstituted aralkylgroup having 7 to 30 carbon atoms, a substituted silyl group, asubstituted germanium group, a substituted phosphine oxide group, afluorine atom, a cyano group, a nitro group, and a carboxy group. 26.The organic electroluminescence device according to claim 25, whereinY₄₁ to Y₄₈ in the formula (35) each independently represent CR₃₂; Y₄₁ toY₄₅, Y₄₇ and Y₄₈ in the formulae (36) and (37) each independentlyrepresent CR₃₂; Y₄₁, Y₄₂, Y₄₄, Y₄₅, Y₄₇, and Y₄₈ in the formula (38)each independently represent CR₃₂; Y₄₂ to Y₄₈ in the formula (39) eachindependently represent CR₃₂; Y₄₂ to Y₄₇ in the formula (30a) eachindependently represent CR₃₂; and a plurality of R₃₂ in the formulae(37) to (39) and (30a) are the same or different.
 27. The organicelectroluminescence device according to claim 25, wherein X₃ in theformulae (37) to (39) and (30a) represents an oxygen atom or a sulfuratom.
 28. The organic electroluminescence device according to claim 1,wherein an ionization potential Ip1 of the first compound and anionization potential Ip2 of the second compound satisfy a relationshipof 0≤Ip2−Ip1≤0.3 eV.
 29. An electronic device comprising the organicelectroluminescence device according to claim 1.